Preheat your oven to 350°F (175°C) and grease a mini muffin tin.

In a bowl, cream together the softened butter and sugar until fluffy. Add the egg, lemon zest, and lemon juice; mix well.

In another bowl, whisk together the flour and a pinch of salt; gradually combine with the wet ingredients until just mixed.

Spoon about 1 tablespoon of dough into each muffin tin cavity and press down slightly.

Bake for 10 minutes until golden; let cool completely before filling with lemon curd.

For the lemon curd, melt butter and sugar over low heat, whisk in egg yolks until thickened; allow to cool before filling cups.