01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a bowl, whisk together flour, baking powder, baking soda, and salt.
03 - In a large bowl, cream butter and sugar until light and fluffy. Beat in eggs, one at a time. Add lemon zest, lemon juice, and vanilla extract; mix well.
04 - Add flour mixture in three additions, alternating with milk, beginning and ending with flour. Mix until just combined.
05 - Divide batter evenly into liners, filling each about 2/3 full. Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean. Cool cupcakes in the pan for 5 minutes, then transfer to a wire rack to cool completely.
06 - In a small saucepan, whisk together egg yolks, sugar, lemon zest, lemon juice, and salt. Cook over medium heat, stirring constantly, until mixture thickens and coats the back of a spoon (about 5-7 minutes). Remove from heat and stir in butter until smooth. Transfer to a bowl, cover with plastic wrap pressed onto the surface, and chill until set.
07 - In a clean, grease-free bowl, beat egg whites and cream of tartar until foamy. Gradually add sugar, one tablespoon at a time, beating until stiff, glossy peaks form. Beat in vanilla.
08 - Use a small knife or cupcake corer to remove a small section from the center of each cupcake. Fill the cavity with chilled lemon curd.
09 - Pipe or spoon meringue onto each filled cupcake, creating swirls or peaks. Toast the meringue with a kitchen torch until golden, or briefly broil in the oven (watch carefully).