Set your oven to 180°C (350°F) and let it fully preheat. This ensures even baking.

Line a 12-well cupcake pan with paper liners to prevent sticking and make cleanup easier.

In a medium bowl, whisk together the all-purpose flour, cake flour, baking powder, and a pinch of salt. This step ensures an even distribution of leavening and seasoning.

In a stand mixer fitted with the whisk attachment, beat the softened butter, sugar, and vanilla extract on medium-high speed. Whip for 3–4 minutes until the mixture is pale, light, and fluffy. This creates an airy base for your cupcakes.

Add the eggs and the additional egg white one at a time, mixing thoroughly after each addition. Scrape down the sides of the bowl to ensure the ingredients are evenly incorporated.

Reduce the mixer speed to low-medium. Gradually add the dry flour mixture in two additions, alternating with the milk. Begin and end with the dry ingredients, mixing just until combined.

Using a rubber spatula, gently fold in the finely chopped strawberries. This ensures the batter stays light and the strawberries are evenly distributed.

Spoon the batter into the prepared liners, filling each one about 3/4 full to allow room for the cupcakes to rise.

Bake in the preheated oven for 25–30 minutes, or until the tops are golden brown. To check doneness, insert a toothpick into the center of a cupcake; it should come out clean.

Remove the pan from the oven and let the cupcakes cool in the pan for 5–10 minutes. Then transfer them to a wire rack to cool completely before frosting.

Place the egg whites and sugar into the mixing bowl. Set the bowl over a pan of simmering water, ensuring the bottom of the bowl doesn’t touch the water. This creates a double-boiler effect, gently heating the mixture.

Stir the mixture constantly as it heats. Continue until the sugar has fully dissolved. To test, rub a bit of the mixture between your fingers—if it feels grainy, it’s not ready yet.

Once the sugar has dissolved, transfer the bowl to your stand mixer fitted with the whisk attachment. Beat on medium-high speed for about 10 minutes, or until stiff peaks form and the mixture has cooled to room temperature (the bowl should feel cool to the touch).

Reduce the mixer speed to medium-low. Begin adding the softened butter, 2 tablespoons at a time. Wait until the butter is fully incorporated before adding more. This process should be gradual to ensure smoothness.

If the mixture appears to “curdle” or separate, don’t worry! Continue beating, and it will come together into a smooth, silky frosting.

Once the butter is fully incorporated, scrape down the sides of the bowl. Add the strawberry purée and continue beating until fully combined. The frosting may curdle again, but this is normal—just keep mixing until it becomes smooth.

Transfer the finished frosting to a piping bag fitted with a star tip. Pipe the buttercream generously onto your cooled cupcakes.

For an extra touch, decorate the cupcakes with fresh strawberry slices or other toppings of your choice.