Preheat the oven to 350°F (180°C.) Grease and line an 8-inch round cake pan with 3-inch high sides. 

Peel and core the apples, then slice them in 1/4-inch slices. Add them to a medium bowl. Toss them with 1/2 tablespoon of lemon juice to avoid browning too much. Set them aside.

Mix the melted butter, oil, sugar, vanilla, and eggs in a large bowl. 

Combine flour, baking powder, and salt in a small bowl, whisk to combine, and then add it to the wet ingredients. Fold them together, along with the milk, until it's combined. There may be a few small lumps of flour, but that's okay.

Pour half the cake batter into the prepared pan.

Arrange half of the apples over the batter, snuggly fitting them on. Spoon over the remaining cake batter and top with the remaining apple slices. It's okay if the individual slices overlap a bit.

Mix the sugar and cinnamon for the topping and generously sprinkle this over the apples.

Bake the cake in the oven for approximately 60-70 minutes until golden brown and a skewer inserted into the middle has no wet batter, just a few moist crumbs.

Remove from the oven and let the cake cool in the pan for approx 10 minutes.

Use a butter knife to loosen the cake's edges from the pan gently, then run the knife around the entire circumference. Place a wire cooling rack or plate on top of the cake pan. Hold it firmly against the pan and carefully flip it over, allowing the cake to release onto the rack or plate. Remove the parchment paper. Add another wire rack on top and carefully flip the cake so it's no longer upside down.

Let the cake cool down to room temperature. Then dust with powdered sugar before serving.