01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
03 - In a large bowl, beat softened butter and granulated sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract and lemon zest.
04 - Gradually add dry ingredients in three portions, alternating with milk. Mix until just combined, being careful not to overmix.
05 - Divide batter evenly among prepared cupcake liners. Bake for 18 to 22 minutes until a toothpick inserted in the center comes out clean. Cool completely before filling.
06 - Whisk together eggs, egg yolks, sugar, lemon juice, and lemon zest in a heatproof bowl. Set over a saucepan of simmering water, stirring constantly until mixture thickens and coats the back of a spoon, about 8 to 10 minutes. Remove from heat and whisk in butter until smooth. Cool completely.
07 - Beat egg whites and cream of tartar in a clean bowl until soft peaks form. Gradually add sugar while beating, continuing until stiff, glossy peaks form. Fold in vanilla extract.
08 - Use a small knife or apple corer to remove the center of each cooled cupcake, creating a well. Fill each cavity with cooled lemon curd.
09 - Pipe or spoon meringue over each filled cupcake, creating decorative peaks. Toast using a kitchen torch until golden brown, or place under broiler for 1 to 2 minutes, watching closely to prevent burning.
10 - Serve immediately or refrigerate until ready to serve.