01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper 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 butter and granulated sugar together using a hand or stand mixer on medium speed until pale, light, and fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition until fully incorporated.
04 - Mix in the lemon zest and fresh lemon juice until evenly combined throughout the batter.
05 - In a small bowl, stir together the milk and sour cream until smooth.
06 - Add the dry ingredient mixture and the milk mixture to the creamed butter in alternating additions, starting and ending with the dry ingredients. Mix on low speed until just combined — do not overmix.
07 - Gently fold the diced fresh strawberries into the batter using a spatula, being careful not to crush the pieces.
08 - Divide the batter evenly among the 12 muffin cups, filling each liner about two-thirds full.
09 - Bake for 16–18 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Transfer the pan to a wire rack and let the cupcakes cool completely before frosting.
10 - Beat the butter on medium speed until smooth and creamy, about 2 minutes. Gradually add the sifted powdered sugar, beating on low speed until incorporated, then increase to medium-high and beat until fluffy. Add the strawberry puree, fresh lemon juice, and salt. Beat until the frosting is light, creamy, and free of lumps.
11 - 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.