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, do not cut 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, watch carefully.
10 - Serve immediately or store in refrigerator for up to 2 days.