Preheat your oven to 350°F. Line a 12-cup muffin tin with paper liners; this recipe yields 12 to 14 cupcakes.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large bowl, beat the softened butter, granulated sugar, and lemon zest together until light and fluffy, about 2 to 3 minutes.

Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.

With the mixer on low speed, add about one-third of the flour mixture to the butter mixture, mixing until just combined. Then mix in the sour cream.

Stop the mixer and scrape down the sides and bottom of the bowl with a spatula.

Beat in another third of the flour mixture, then add the milk and mix until just incorporated. Do not overmix.

Scrape down the bowl again, then beat in the remaining flour mixture until no streaks remain.

Gently stir in the fresh lemon juice. If you see any lumps, whisk the batter briefly until smooth.

Divide the batter evenly among the prepared liners, filling each about two-thirds to three-quarters full.

Bake one tin at a time in the center of the oven for 15 to 18 minutes, or until a toothpick inserted in the center comes out clean. Let the cupcakes cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Core the strawberries to remove the white centers, then place them in a food processor or blender. Pulse until you have a smooth puree.

Pour the puree through a fine-mesh sieve set over a bowl, using the back of a spoon or a rubber spatula to push it through. Discard the seeds. You may need to do this in batches.

Transfer the seedless puree to a small saucepan and place it over low to medium heat. Bring to a gentle boil, stirring occasionally. As it cooks, the puree will thicken and darken in color.

Continue cooking until the puree has reduced to about 1/4 cup and has a jam-like consistency, roughly 15 minutes. Remove from heat and let cool completely. To speed cooling, place the puree in a small bowl or jar and refrigerate.

In a large bowl, beat the softened butter on medium speed until creamy and smooth, about 2 minutes.

Add 2 cups of powdered sugar and beat on low speed until combined, then increase speed to medium and beat for another minute.

Add 2 to 3 tablespoons of the cooled strawberry reduction and beat until fully incorporated.

Gradually add the remaining powdered sugar, about 1/2 cup at a time, beating well after each addition. If the frosting becomes too thick, add 1 tablespoon of heavy cream. If it becomes too thin, stop adding strawberry reduction. Adjust sweetness and consistency to your liking.

Once the frosting is smooth and spreadable, use it immediately to frost the completely cooled cupcakes. You can spread it with a knife or pipe it using a piping bag fitted with a 1M tip.