- 4 lemons, freshly zested (about 2-3 tablespoons)
- 1 cup sugar
- 1/2 cup (1 stick) butter, melted
- 1 3/4 cup all-purpose flour
- 1 1/2 teaspoons baking powder
- 1/2 cup milk
- 1/2 cup sour cream
- 1 teaspoon vanilla
- 2 large egg whites
- 1 cup blackberries
- 2 tablespoons lemon juice
- 1 cup (2 sticks) butter, room temperature
- 4 cups powdered sugar
- 1 teaspoon vanilla
- 1 tablespoon milk or cream
- In a large mixing bowl, add lemon zest and sugar. Combine them by rubbing it together between your fingers. The sugar will look slightly fluffy when you're done, and you shouldn't see any large chunks of lemon zest.
- Add the melted butter to the sugar mixture. Cream mixture until fluffy and combined.
- Sift together flour and baking powder, and add to the sugar mixture, beating until combined.
- In a separate bowl, add milk, sour cream, vanilla, and egg whites. Whisk together.
- Add the milk mixture to the flour and sugar mixture, and beat at medium speed, just until combined. Mixing too much will cause the cupcakes to be too firm.
- Line a greased muffin tin with cupcake liners. Divide the cupcake batter evenly between 12 molds. (I probably used a quarter to a third cup of batter per cupcake). Bake in a 350° oven for 15-19 minutes, or until a toothpick inserted into the top comes out clean. Allow to cool completely before frosting.
- Add blackberries and lemon juice to a small saucepan. Over medium heat, bring mixture to a simmer, stirring often. Your blackberries will become soft enough that they will basically mash themselves while you're mixing. Simmer for about 20 minutes, or until you have about ? cup of blackberry puree mixture.
- If you don't want seeds or skins in your buttercream, strain the blackberry puree through a fine mesh strainer at this point. (I did not strain mine, but did run it through a food processor to make sure it was extra smooth) Allow to cool to room temperature
- In a large mixing bowl, add butter and blackberry puree. Beat together with a mixer until mixture is smooth.
- Add in the powdered sugar, and beat on medium-high until mixture is smooth and creamy.
- Add your milk or cream and vanilla and beat again to combine. Test your buttercream now. If it's still too thick, continue adding milk or cream, 1 tablespoon at a time until buttercream reaches desired consistency.
- You can frost your cupcakes with the blackberry buttercream as soon as they are completely cooled. You can spread or pipe it on. I used 1m tip.