1. Preheat oven to 350°F and line muffin tin with cupcake liners.

2. In a medium bowl, whisk flour, baking powder, and salt; set aside.

3. Cream butter and sugar until light and fluffy (about 2 minutes).

4. Add eggs and vanilla; beat 1 minute until well combined.

5. Alternate adding flour mixture and milk, beginning and ending with flour. Mix just until combined.

6. Divide batter into 12 cupcake liners and bake for 18–20 minutes.

7. Cool in pan 5 minutes, then transfer to a rack to cool completely.

8. While baking, prepare lemon curd by whisking egg yolks, sugar, zest, juice, and salt over low heat for 10–12 minutes, stirring constantly until thick.

9. Remove from heat, stir in butter, and let cool with plastic wrap on surface.

10. Make frosting by beating butter until fluffy, then gradually add sugar and lemon juice until smooth and spreadable.

11. Use a paring knife or piping tip to cut a small well into each cooled cupcake.

12. Pipe a ring of frosting around the edge and fill each center with lemon curd.

13. Chill cupcakes for 15–20 minutes to set before serving.