01 - Preheat oven to 350°F. Line a standard 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. Set aside.
03 - In a large mixing bowl, beat the room-temperature butter and granulated sugar together using an electric mixer on medium-high speed until the mixture is pale, light, and fluffy, about 3 minutes.
04 - Add the eggs one at a time, beating well after each addition until fully incorporated 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 whole milk and sour cream until smooth.
07 - Alternately add the flour mixture and the milk-sour cream mixture to the creamed butter, beginning and ending with the dry ingredients. Mix on low speed until just combined, being careful not to overmix.
08 - Gently fold the diced fresh strawberries into the batter using a spatula, distributing them evenly without crushing.
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 before frosting.
11 - Beat the room-temperature butter on medium speed until smooth and creamy. Gradually add the sifted powdered sugar, beating until fully incorporated and fluffy. Blend in the strawberry puree, fresh lemon juice, and pinch of salt, then beat on medium-high speed until the frosting is light and airy.
12 - Pipe or spread the buttercream generously onto the fully cooled cupcakes. Garnish with additional fresh strawberries or a sprinkle of lemon zest if desired.