01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
03 - In a large bowl, beat butter and sugar together until light and fluffy. Add eggs one at a time, mixing well after each. Stir in lemon zest and vanilla.
04 - Combine milk and lemon juice. Add dry ingredients to the butter mixture in three parts, alternating with the milk-lemon juice mixture, starting and ending with dry ingredients. Mix until just combined.
05 - Divide batter evenly among cupcake liners about 3/4 full. Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean. Cool completely on a wire rack.
06 - In a small saucepan over medium heat, whisk egg yolks, sugar, lemon juice, and zest. Cook, stirring constantly, until thickened about 5–7 minutes. Remove from heat and stir in butter until smooth. Transfer to a bowl and cool completely.
07 - Once cupcakes and curd are cool, use a small knife or cupcake corer to remove the center of each cupcake without cutting all the way through. Fill each cavity with about 1 teaspoon lemon curd.
08 - In a heatproof bowl over a pot of simmering water, whisk egg whites and sugar constantly until sugar dissolves and mixture is warm to the touch about 3 minutes. Remove from heat. Add cream of tartar and beat with an electric mixer until stiff, glossy peaks form. Beat in vanilla.
09 - Pipe or spoon meringue onto filled cupcakes. Toast meringue using a kitchen torch, or place cupcakes under the broiler for 1–2 minutes until golden, watching carefully.
10 - Serve immediately or store in refrigerator for up to 2 days.