Make the Cupcakes:

1. Preheat oven to 350°F (175°C). Line a muffin tin with 12 liners.

2. In a bowl, whisk together flour, baking powder, baking soda, and salt.

3. In a separate bowl, beat butter and sugar until light and fluffy (2–3 minutes).

4. Add eggs one at a time, beating well. Mix in vanilla, lemon zest, and lemon juice.

5. Alternately add flour mixture and buttermilk, starting and ending with flour.

6. Fill liners about ⅔ full and bake for 16–18 minutes, or until a toothpick inserted comes out clean.

7. Let cupcakes cool completely on a wire rack before filling.

Make the Lemon Curd:

1. In a small saucepan over medium heat, whisk together egg yolks, sugar, lemon juice, and zest.

2. Stir constantly for 6–8 minutes, until mixture thickens and coats the back of a spoon.

3. Remove from heat and whisk in butter until smooth. Let cool to room temperature, then refrigerate.

Assemble:

1. Once cupcakes are cool, cut out the center of each using a small knife or cupcake corer.

2. Spoon or pipe cooled lemon curd into the hollowed centers.

3. Frost with lemon buttercream or whipped topping if desired.