• Preheat the oven to 425°F/220°C. Grease or line a standard muffin pan with 12 paper liners.

Streusel

• In a small bowl combine melted butter, granulated sugar, and all-purpose flour. Use a fork to combine it into a coarse crumb, then set it aside. 45 g unsalted butter, melted, 63 g all-purpose flour, 65 g granulated sugar, Pinch of salt

Batter

• Mix the all-purpose flour, baking powder, baking soda, and salt in a bowl. Set aside. 250 g all-purpose flour, 2 teaspoons baking powder, 3/4 tsp salt , 1/4 tsp baking soda
• In a large bowl add granulated sugar and lemon zest. Use your fingers to rub the zest into the sugar to release the lemon oils. 150 g granulated sugar, 1 Tablespoon lemon zest
• Add the melted butter, eggs, vanilla and buttermilk. Whisk until well-combined. 113 g unsalted butter, melted and slightly cooled, 2 large eggs, 1 Tablespoon lemon juice, 1 teaspoon vanilla paste, 180 g buttermilk
• Fold in the dry ingredients until almost combined, then add the blueberries and fold all together. If using frozen blueberries, give these a good rinse under cold water first and drain before adding. 260 g blueberries
• Divide the batter evenly over the 12 muffin liners.
• Generously pile the streusel on top of each muffin.

Baking

• Bake the muffins at 425°F/220°C for 5 minutes, then turn the oven down to 350°F/180°C and continue baking for another 20 minutes or until the tops of the muffins are golden brown and spring back when lightly pressed in the center.
• Remove them from the oven and let the muffins cool in the pan for 10 minutes before removing and placing them on a wire rack to cool to room temperature.