Preheat the oven and prepare the cupcake tins.

In a mixing bowl, cream together the softened butter and sugar.

Add the eggs one at a time, mixing well after each addition.

Stir in the buttermilk, lemon zest, and lemon juice.

In a separate bowl, combine the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Pour the batter into cupcake tins, filling them about ⅔ full.

Bake in the preheated oven for 20 minutes or until a toothpick inserted comes out clean.

Let the cupcakes cool completely on a wire rack before frosting.

For the lemon buttercream, beat together the softened butter, powdered sugar, lemon juice, and lemon zest until fluffy.

Add milk as needed for consistency and frost the cooled cupcakes.