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