01 - Preheat oven to 350°F. Line a 12-cup muffin tin with cupcake 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 until pale, light, and fluffy, about 3 minutes.
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.
06 - Stir together the milk and sour cream in a small bowl 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 until just combined; do not overmix.
08 - Gently fold the diced strawberries into the batter using a spatula, taking care 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 butter on medium speed until smooth and creamy. Gradually add the sifted powdered sugar, beating until fully incorporated and fluffy. Add the strawberry puree, lemon juice, and salt, then beat until light and creamy.
12 - Pipe or spread the buttercream onto the fully cooled cupcakes. Garnish with fresh strawberries or additional lemon zest if desired.