01 - Preheat 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 unsalted butter and granulated sugar together using a hand or stand mixer on medium speed until the mixture is pale, light, and fluffy.
04 - Add the eggs one at a time, beating well after each addition to ensure full incorporation 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 - 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 to avoid overworking the batter.
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 cool completely.
11 - Beat the unsalted 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, then beat until the frosting is light and creamy.
12 - Pipe or spread the buttercream onto the fully cooled cupcakes. Garnish with additional fresh strawberries or lemon zest if desired.