01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a medium bowl, whisk together the flour, baking powder, and salt until evenly distributed.
03 - In a large bowl, beat the butter and granulated sugar together using an electric mixer on medium-high speed until pale, light, and fluffy, about 3 minutes.
04 - Add the eggs one at a time, beating well after each addition and scraping down the sides of the bowl as needed.
05 - Mix in the lemon zest and fresh lemon juice until fully incorporated.
06 - In a small bowl, stir together the milk and sour cream until smooth.
07 - Alternate adding the dry ingredient mixture and the milk mixture to the creamed butter, beginning and ending with the dry ingredients. Mix on low speed until just combined — do not overmix.
08 - Gently fold the diced 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 16–18 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 - In a mixing bowl, beat the 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 salt; beat on medium-high speed until the frosting is light and creamy.
12 - Pipe or spread the buttercream generously onto the fully cooled cupcakes. Garnish with fresh strawberry halves or additional lemon zest if desired.