01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a bowl, whisk together flour, baking powder, and salt.
03 - In a large bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, then mix in vanilla and lemon zest.
04 - Alternately add dry ingredients and milk, beginning and ending with dry ingredients. Mix until just combined.
05 - Divide batter evenly among liners. Bake 18-20 minutes, or until a toothpick inserted comes out clean. Cool completely.
06 - In a heatproof bowl, whisk lemon juice, zest, sugar, and eggs. Place over a saucepan of simmering water and cook, whisking constantly, until thickened (about 8-10 minutes). Remove from heat, whisk in butter until smooth, then chill.
07 - In a clean bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating until stiff, glossy peaks form. Beat in vanilla.
08 - Use a paring knife or apple corer to remove a small core from each cupcake center. Fill each with about 1 teaspoon lemon curd. Pipe or spoon meringue on top.
09 - Toast meringue with a kitchen torch or under a broiler for 1-2 minutes until golden. Serve immediately or refrigerate.