Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.

In a large bowl, whisk together the all-purpose flour, baking powder, and salt.

In a separate bowl, cream the unsalted butter and granulated sugar together until smooth. Add eggs and vanilla, mixing until fully incorporated.

Gradually mix in the flour mixture and milk alternately, ending with flour.

Fill the cupcake liners three-quarters full with the batter and bake for 18-20 minutes.

Cool in the pan for 5 minutes then transfer to a wire rack to cool completely.

For the lemon curd, whisk together egg yolks, sugar, zest, juice, and salt in a saucepan over low heat until thickened.

Remove from heat and whisk in butter, cover with plastic wrap to cool.

To prepare the frosting, beat softened butter, gradually add powdered sugar, and lemon juice until fluffy.

Once cooled, hollow out the centers of the cupcakes, pipe frosting around the edges, and fill with lemon curd.

Chill in the refrigerator for 15-20 minutes before serving.