Moist 6-inch Chocolate Cake (single layer)

This 6-inch chocolate cake is a single-layer chocolate cake with a moist, fudgy crumb and a smooth, silky chocolate Swiss meringue buttercream. It serves 6 to 8 people, which makes it perfect for a small gathering or when you just don’t want a towering layer cake sitting on the counter.

A 6-inch cake is one of the most useful sizes to have in your repertoire. It’s generous enough for a small celebration but not so big that you’re eating leftovers for a week. This one has everything you’d want from a chocolate cake: a deeply chocolatey, moist crumb from the combination of cocoa powder and hot coffee, and a frosting that tastes like chocolate mousse rather than a sugar hit.

The frosting is a chocolate Swiss meringue buttercream. It’s less sweet than American buttercream, incredibly smooth, and pairs perfectly with the cake. If you have leftover egg yolks from making it, these egg yolk cookies are a great use for them.

Ingredients and why

For the cake:

1. All-purpose flour: The base of the batter.
2. Cocoa powder: Natural or Dutch-processed both work here. Natural cocoa gives a slightly deeper, more intense chocolate flavor.
3. Baking powder and baking soda: Both are used for lift. The vinegar in the batter reacts with the baking soda specifically, so don’t leave it out.
4. Egg: One large egg for structure.
5. Granulated sugar and brown sugar: Used together. The brown sugar adds moisture and a little depth alongside the regular sugar.
6. Oil: Vegetable oil or melted coconut oil. Oil produces a moister crumb than butter in this style of cake.
7. Apple cider vinegar: Just half a teaspoon. It adds acidity for a tender, lighter crumb and reacts with the baking soda for rise.
8. Whole milk: Adds moisture and richness to the batter.
9. Hot coffee: Used to bloom the cocoa. If you’d rather not use coffee, hot water works fine.

For the chocolate Swiss meringue buttercream:

10. Egg whites: Two large egg whites, heated with sugar over a double boiler.
11. Granulated sugar: Dissolved into the egg whites over heat before whipping.
12. Unsalted butter: Must be properly softened to room temperature. Cold butter makes the buttercream curdle; warm butter makes it soupy.
13. Semi-sweet chocolate: Melted and cooled to room temperature before adding. This is what gives the frosting its deep chocolate flavor.

Crucial tip: The butter for the buttercream needs to be genuinely at room temperature, not just slightly softened. Press a finger into a cube and it should give easily with no resistance. If it’s still cool and firm, the buttercream will look curdled and take a long time to come together.

Method

Prepare your pan

1. Preheat the oven to 350°F (180°C). Grease and line a 6×3-inch round cake pan with parchment paper

Make the cake batter

1. Whisk together the flour, cocoa powder, baking powder, baking soda, and salt in a bowl until evenly combined with no lumps. Set aside.

1. In a separate bowl, whisk together the egg, sugars, vanilla, and oil. Measure out the milk, add the vinegar, stir, and leave it to sit for a couple of minutes.

1. Add the dry ingredients to the wet in thirds, alternating with the milk, folding gently with a spatula after each addition.

1. Pour in the hot coffee and fold it in until everything is well combined, but don’t over-mix it.

1. Pour into the prepared pan and bake for 30 to 35 minutes, until a skewer inserted in the center comes out clean. Cool in the pan for 15 minutes, then turn out onto a wire rack and cool completely before frosting.

The frosting

1. Melt the chocolate and set aside to cool to room temperature.
2. Combine the egg whites and sugar in a clean metal bowl (the bowl of your stand mixer or another metal bowl) and set over a pot of gently simmering water.
3. Whisk constantly until the sugar has dissolved and the mixture reaches 160°F (71°C). Transfer to your stand mixer if needed, fit the whisk attachment, and beat on medium-high until stiff glossy peaks form and the bowl is cool to the touch.
4. Add the softened butter one cube at a time with the mixer running. Beat in the cooled chocolate and vanilla. Switch to the paddle and beat on low for 5 to 10 minutes.

1. Spread the buttercream generously over the top and sides of the cooled cake.

1. Decorate how you like!

Swiss meringue buttercream tips

• If the buttercream looks curdled or lumpy: The butter was probably too cold. Keep beating on medium-high and it will come together. This can take several minutes so don’t give up.
• If the buttercream looks soupy or greasy: The meringue was too warm when the butter went in. Refrigerate the bowl for 10 minutes, then re-whip.
• If the meringue won’t whip to stiff peaks: Check that the bowl and whisk are completely clean and free of any grease. Any trace of fat will stop the whites from whipping properly.

Check out the full Chocolate Swiss Meringue Buttercream recipe with detailed instructions.

Storing

Store leftover cake at room temperature in an airtight container for up to 3 days, or refrigerate for up to 5 days. The buttercream will firm up in the fridge, so let the cake sit at room temperature for about an hour before serving.

The unfrosted cake layer can be wrapped tightly and frozen for up to 3 months. The buttercream can also be frozen for up to 3 months. Thaw both in the fridge overnight, then bring to room temperature before assembling. Refrigerated or frozen buttercream will need to be re-whipped to bring it back to a fluffy consistency.

More cake recipes

• Egg White Chocolate Cake: a two-layer 8-inch version using egg whites in both the cake and frosting
• 6-Inch Red Velvet Cake: small batch with cream cheese frosting
• 8-Inch Vanilla Cake: a classic, reliable vanilla layer cake
• Easy French Pear Cake: simple, rustic, and ready in under an hour

Happy baking!

Moist 6-inch Chocolate Cake (Single layer)

Elien Lewis

This 6-inch chocolate cake is a moist single-layer chocolate cake frosted with a chocolate Swiss meringue buttercream frosting.

5 from 29 votes

Print Recipe Pin Recipe

Prep Time 20 minutes mins

Cook Time 30 minutes mins

Total Time 50 minutes mins

Course Cakes

Cuisine American

Servings 8 people

Calories 322 kcal

Ingredients

 

MetricUS Customary

 

1x2x3x

• 83 g all-purpose flour
• 25 g cocoa powder natural or dutch processed
• 1/2 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/4 teaspoon salt
• 60 g whole milk
• 1/2 teaspoon Apple cider vinegar or white vinegar or lemon juice
• 1 large egg
• 66 g granulated sugar
• 50 g soft brown sugar
• 45 g oil vegetable or melted coconut oil
• 1/2 teaspoon vanilla paste or extract
• 60 g hot coffee or use hot water

Chocolate Swiss meringue buttercream

• 113 g semi-sweet chocolate
• 2 large egg whites 60g/2 oz
• 66 g granulated sugar
• Pinch salt
• 170 g unsalted butter softened to room temperature.
• 1/2 teaspoon vanilla paste or extract

Instructions

 

Cake

• Preheat the oven to 350°F (180°C). Grease and line a 6×3-inch round cake pan with parchment paper.
• Whisk together the flour, cocoa powder, baking powder, baking soda, and salt in a bowl. Set aside. 83 g all-purpose flour, 25 g cocoa powder, 1/2 teaspoon baking powder, 1/4 teaspoon baking soda, 1/4 teaspoon salt
• Measure the milk, add the vinegar, stir, and leave to sit for 2 minutes. 60 g whole milk, 1/2 teaspoon Apple cider vinegar
• In a separate bowl, whisk together the egg, sugars, oil, and vanilla. 1 large egg, 66 g granulated sugar, 50 g soft brown sugar, 45 g oil, 1/2 teaspoon vanilla paste or extract
• Add the dry ingredients to the wet in thirds, alternating with the milk mixture, folding gently with a spatula after each addition.
• Pour in the hot coffee and fold until just combined. Do not overmix. 60 g hot coffee
• Pour the batter into the prepared pan and bake for 30 to 35 minutes, until a skewer inserted in the center comes out clean.
• Run a knife around the edge to loosen. Cool in the pan for 15 minutes, then turn out onto a wire rack and cool completely before frosting.

Chocolate Swiss Meringue Buttercream

• Melt the chocolate in a microwave-safe bowl in 20 to 30 second bursts, stirring after each, until fully melted. Set aside to cool to room temperature. 113 g semi-sweet chocolate
• In a clean, grease-free metal bowl (either the bowl of your stand mixer or another metal bowl), combine the egg whites, sugar, and salt. Set over a pot with 1 inch of gently simmering water, making sure the bottom of the bowl does not touch the water. Do not use a glass or ceramic bowl as it can crack or shatter. Whisk constantly until all the sugar has dissolved and the mixture reaches 160°F (71°C) on an instant-read thermometer. 2 large egg whites, 66 g granulated sugar, Pinch salt
• If you used a separate metal bowl, transfer the mixture to the bowl of your stand mixer now. Fit the whisk attachment and beat on medium-high speed until stiff, glossy peaks form and the bowl is completely cool to the touch, about 8 to 10 minutes.
• With the mixer running on medium speed, add the softened butter one cube at a time, waiting until each cube is fully incorporated before adding the next. The mixture may look curdled at this stage. Keep beating and it will come together.170 g unsalted butter
• Beat in the cooled melted chocolate and vanilla until the buttercream is smooth and fluffy. 1/2 teaspoon vanilla paste
• Switch to the paddle attachment and beat on low speed for 5 to 10 minutes to remove the larger air bubbles.

Assemble

• Spread the buttercream generously over the top and sides of the cooled cake. Decorate as desired. Store leftover cake at room temperature in an airtight container for up to 3 days, or refrigerate for up to 5 days.

Notes

• Coffee: Substitute hot water if preferred. The finished cake will not taste like coffee.
• Buttercream troubleshooting: If the buttercream looks curdled, keep beating and it will come together. If it looks soupy, refrigerate the bowl for 10 minutes then re-whip.
• Clean equipment: The bowl and whisk must be completely grease-free before whipping the egg whites or they will not whip properly.
• Storage: Unfrosted cake can be wrapped and frozen for up to 3 months. Buttercream can also be frozen for up to 3 months. Thaw in the fridge overnight, bring to room temperature, and re-whip the buttercream before using.
• Leftover egg yolks: Use them in these egg yolk cookies.

Nutrition

Serving: 1sliceCalories: 322kcalCarbohydrates: 34gProtein: 3gFat: 21gSaturated Fat: 10gPolyunsaturated Fat: 9gTrans Fat: 1gCholesterol: 31mgSodium: 261mgFiber: 2gSugar: 23g

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