Preheat oven to 350 degrees F.
Grease or place parchment paper on two baking sheets.
In a medium mixing bowl, stir flour, salt, and baking powder together, set aside.
In an stand mixture, cream butter and sugar togethers until light and fluffy.
Add the eggs, vanilla, lemon juice and lemon zest.
Next add the dry ingredients, 1/3 at a time, mixing well in between each addition.
Drop Tablespoon sized dough onto cookie sheets.
Bake 10-12 minutes, until lightly golden brown.
Cool on baking sheets 5 minutes before moving to cooling rack to cool completely.
To make buttercream in stand mixer cream butter until fluffy. Add in powdered sugar and mix again until creamy and smooth.
Lastly add the lemon zest and lemon juice and mix again.
Add buttercream to a piping bag and pipe onto one cookie (you can use a knife and spread on if you don’t have a piping bag). Place another cookie on top.
Repeat with remaining cookies.