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 becomes pale, light, and fluffy—about 3 minutes.
04 - Add the eggs one at a time, beating thoroughly after each addition until fully incorporated before adding the next.
05 - Mix in the fresh lemon zest and lemon juice until evenly combined throughout the batter.
06 - In a small bowl, stir together the milk and sour cream until smooth and well blended.
07 - With the mixer on low speed, alternate adding the dry flour mixture and the milk-sour cream mixture to the creamed butter, beginning and ending with the dry ingredients. Mix until just combined—do not overmix.
08 - Using a spatula, gently fold the diced fresh strawberries into the batter with careful, sweeping motions to avoid breaking the fruit pieces.
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 16–18 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.
11 - In a mixing bowl, 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, creamy, and spreadable.
12 - Pipe or spread the strawberry lemonade buttercream generously onto each fully cooled cupcake. Garnish with additional fresh strawberry slices or a sprinkle of lemon zest if desired.