Preheat the oven to 350°F (175°C).

In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs, lemon zest, lemon juice, and vanilla extract, mixing until well combined.

In a separate bowl, whisk together the flour and baking powder.

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

Drop spoonfuls of dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Bake for 10-12 minutes or until the edges are lightly golden.

Remove from the oven and let cool completely.

In a mixing bowl, combine the softened butter and powdered sugar.

Add the lemon juice and lemon zest, mixing until smooth and creamy.

Once the cookies are completely cooled, spread the frosting generously on top of each cookie.

Let the frosting set for a few minutes before serving.