01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, and salt until evenly distributed.
03 - In a large bowl, beat the room-temperature butter and granulated sugar together using a hand or stand mixer until the mixture is light and fluffy.
04 - Add the eggs one at a time, beating well after each addition until fully incorporated.
05 - Mix in the lemon zest and fresh lemon juice until evenly combined throughout the batter.
06 - In a small bowl, stir together the milk and sour cream until smooth.
07 - Alternate adding the dry ingredient mixture and the milk-sour cream mixture to the creamed butter, beginning and ending with the dry ingredients. Mix until just combined—do not overmix.
08 - Gently fold the diced fresh strawberries into the batter using a spatula, being careful not to overmix.
09 - Divide the batter evenly among the prepared muffin cups, filling each liner about two-thirds full.
10 - Bake for 16 to 18 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Transfer to a wire rack and let cool completely.
11 - Beat the room-temperature butter on medium speed until smooth and creamy. Gradually add the sifted powdered sugar, beating until fully incorporated and fluffy. Add the strawberry puree, fresh lemon juice, and a pinch of salt, then beat until the frosting is light and creamy.
12 - Pipe or spread the strawberry lemonade buttercream onto the fully cooled cupcakes. Garnish with additional fresh strawberries or a sprinkle of lemon zest if desired.