Preheat oven to 350°F (175°C). Line a cupcake pan with liners.
In a bowl, whisk together flour, baking powder, and salt.
In another bowl, beat butter and sugar until fluffy. Add eggs one at a time, then vanilla.
Alternate adding flour mixture and milk to the butter mixture, beginning and ending with flour.
Fill cupcake liners ⅔ full and bake for 18-20 minutes. Let cool.
For lemon curd, whisk lemon juice, zest, sugar, and eggs in a saucepan over medium heat.
Add butter and cook until thickened. Strain and cool.
Fill cooled cupcakes with lemon curd and serve.