Step 1: Preheat and Prepare

Start by preheating your oven to 350°F (177°C) if you’re using a convection oven, or 325°F (163°C) for a conventional oven. Line a mini muffin tin with cupcake liners, ideally in a light-colored pan, as this will help prevent over-browning.

Step 2: Mix Dry Ingredients

In a medium-sized bowl, whisk together your cake flour, baking powder, salt, and sugar. Make sure all dry ingredients are evenly distributed to ensure your cupcakes rise properly.

Step 3: Incorporate Wet Ingredients

Pour in the melted butter and mix until well combined. Next, add the egg white and vanilla extract, stirring until the mixture becomes smooth. Add the milk and sour cream, and gently fold the ingredients together until the batter is smooth and lump-free.

Step 4: Fill the Muffin Tin

Using a spoon or piping bag, fill each mini cupcake liner about ¾ of the way full. Be careful not to overfill, as this will cause the cupcakes to overflow as they bake.

Step 5: Bake to Perfection

Bake your cupcakes for 10-12 minutes. To check if they’re done, gently press the center of a cupcake—if it springs back, they’re ready! Don’t rely on a golden-brown color, as this recipe is designed to keep the cupcakes light and pale.

Step 6: Cool and Prepare Frosting

Once out of the oven, let the cupcakes cool in the pan for about 10 minutes before transferring them to a cooling rack. Allow them to cool completely before adding the buttercream frosting.

Step 7: Make the Buttercream Frosting

In a stand mixer, whip the room-temperature butter for about 5 minutes until it’s light and fluffy. Slowly add the powdered sugar and vanilla extract, and continue to mix on low speed. Once combined, increase the mixer speed to medium-high for another 5 minutes. Add heavy whipping cream, one tablespoon at a time, until the frosting reaches the desired consistency. Pipe the frosting onto the cooled cupcakes and decorate as desired.