01 - Preheat 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 mixing bowl, beat the room-temperature butter and granulated sugar together using a hand or stand mixer on medium speed until pale, light, and fluffy, about 3 minutes.
04 - Add the eggs one at a time, beating well after each addition to ensure full emulsification before adding the next.
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 - Alternately add the dry ingredient mixture and the milk-sour cream blend to the creamed butter mixture in three additions, beginning and ending with the dry ingredients. Mix on low speed until just combined—do not overmix.
08 - Using a spatula, gently fold the diced strawberries into the batter with minimal strokes to preserve the airiness and prevent the fruit from breaking down.
09 - Divide the batter evenly among the prepared muffin cups, filling each liner approximately two-thirds full to allow room for rising.
10 - Bake for 16 to 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.
11 - In a mixing bowl, beat the room-temperature butter on medium speed until smooth and creamy. Gradually add the sifted powdered sugar, beating on low speed until incorporated, then increase to medium-high and beat until fluffy. Blend in the strawberry puree, fresh lemon juice, and a pinch of salt until the frosting is light, creamy, and uniform in color.
12 - Pipe or spread the buttercream generously onto each fully cooled cupcake. Garnish with fresh strawberry halves or additional lemon zest if desired.