Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners.
In a bowl, whisk together flour, sugar, baking powder, and salt.
In another bowl, beat butter until creamy. Add eggs one at a time, then vanilla.
Alternate adding dry ingredients and milk to the butter mixture, starting and ending with dry ingredients.
Fill cupcake liners ⅔ full and bake for 18-20 minutes. Let cool.
For lemon curd, whisk lemon juice, zest, sugar, and egg yolks in a saucepan. Cook over medium heat until thickened. Stir in butter. Let cool.
For meringue, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar and beat until stiff peaks form.
Cut a small hole in the center of each cupcake and fill with lemon curd. Pipe meringue on top and toast with a kitchen torch if desired.