01 - Preheat oven to 350°F. Line a standard 12-cup muffin tin with paper liners and set aside.
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 room-temperature butter and granulated sugar together using a hand or stand mixer 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 - Alternately add the dry ingredient mixture and the milk-sour cream mixture to the creamed butter, 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, taking care not to crush the pieces or overwork the batter.
08 - Divide the batter evenly among the prepared muffin cups, filling each liner about two-thirds full.
09 - 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 before frosting.
10 - Beat the room-temperature 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 a pinch of salt, then beat on medium-high speed until the frosting is light and creamy.
11 - Pipe or spread the buttercream generously onto the completely cooled cupcakes. Garnish with additional fresh strawberries or a sprinkle of lemon zest if desired.