01 - Preheat oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
02 - In a bowl, whisk together flour, baking powder, baking soda, and salt until well combined.
03 - In a large bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Stir in lemon zest and juice.
04 - Add flour mixture in three parts, alternating with milk. Mix until just combined, being careful not to overmix.
05 - Divide batter evenly among cupcake liners. 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 heatproof bowl, whisk together eggs, sugar, lemon juice, and zest. Place bowl over a saucepan of simmering water, creating a double boiler. Whisk constantly until thickened, about 8 minutes. Remove from heat and stir in butter until smooth. Cool completely.
07 - Using a small knife or apple corer, remove the center of each cooled cupcake to create a cavity. Fill each cavity with cooled lemon curd.
08 - In a clean, dry bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar while continuing to beat until stiff, glossy peaks form. Fold in vanilla extract.
09 - Pipe or spoon meringue onto filled cupcakes. Toast meringue under a broiler for 1-2 minutes or use a kitchen torch until golden brown and lightly charred.
10 - Serve immediately or refrigerate for up to 2 days. Store in refrigerator if not serving right away.