Blackberry Lemon Cupcakes

Ingredients:

• 1 and 3/4 cups  cake flour
• 3/4 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/4 teaspoon salt
• 1/2 cup  unsalted butter, softened to room temperature
• 1 cup granulated sugar
• 3 large egg whites, at room temperature
• 2 teaspoons pure vanilla extract²
• seeds scraped from 1/2 of a vanilla bean
• 1/2 cup  full-fat sour cream at room temperature
• 1/2 cup whole milk at room temperature

Directions:

1. Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners. Line a second pan with 2 liners - this recipe makes about 14 cupcakes. Set aside.
2. Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.
3. Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy - about 1 minute. Add the sugar and beat on high speed for 2 minutes until creamed together. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Add the egg whites, vanilla extract, and vanilla bean. Beat on medium-high speed until combined, then beat in the sour cream. Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, add the dry ingredients until just incorporated. With the mixer still running on low, slowly pour in the milk until combined. Do not overmix. You may need to whisk it all by hand to make sure there are no lumps at the bottom of the bowl. The batter will be slightly thick.
4. Pour/spoon the batter into the liners - fill only 2/3 full to avoid spilling over the sides. Bake for 19-22 minutes, or until a toothpick inserted in the center comes out clean. 
5. Top with Buttercream frosting and a blackberry
   

For the Buttercream

•  1 cup fresh blackberries
•  1 tablespoon water
•  1 tablespoon lemon juice
•  1 cup 2 sticks butter, softened
•  4 cups powdered sugar
•  2-4 tablespoons heavy cream or milk
•  1 teaspoon vanilla
•  pinch of salt
• Additional blackberries for garnish if desired

Instructions

• To make the buttercream, place the blackberries, lemon juice and water in a small saucepan. Heat on medium heat stirring occasionally until the blackberries soften and release their juice. Crush the blackberries and continue to cook the mixture on the stove to reduce it. When the mixture coats the back of the spoon, remove from the heat and strain the mixture in a fine mesh strainer to remove the seeds and fruit. You should have roughly 1/4 cup of liquid. Let cool completely
• Beat the softened butter in a stand mixer for 2-3 minutes until light in color and fluffy. Beat in the powdered sugar, vanilla, blackberry reduction and enough of the heavy cream or milk to make a spreadable consistency. Beat the frosting on high for 3-4 minutes or until very fluffy. Pipe the frosting onto cooled cupcakes and garnish with a blackberry if desired.