Preheat the oven to 350° and line a cookie sheet with parchment paper. In a medium bowl combine flour, baking soda, baking powder and salt and set aside.
In a larger bowl, beat the butter and sugar with a hand mixer until light and fluffy. Add in the egg and vanilla extract and mix to combine.
Add in the dry ingredients to the wet ingredients slowly, about 1 cup at a time. Beat using a hand mixer to mix. Divide the dough into 4 bowls, add about 2-3 drops of the food coloring to each one, 2-3 drops of pink in one bowl, 2-3 drops of blue in another bowl etc.
I used clean beaters and used the hand mixer once again to combine the cookie dough with the food coloring. Just make sure to wash them each time before mixing each color.
Scoop about 1 teaspoon of dough and roll into a ball and place on the cookie sheet, leaving about 1 ½ inches apart from each dough ball.
Bake in the preheated oven for 8-10 minutes or until the edges are slightly golden brown. Let them cool for a few minutes before transferring them to a wire rack to cool completely.
While the cookies cool make the buttercream frosting. In a separate mixing bowl add 2 sticks of butter and 3 cups of powdered sugar and beat together using a hand mixer. Add the other 3 cups of powdered sugar and mix again. Add in the vanilla extract and beat until it’s a pale color and fluffy, about 3 minutes.
8. Once the cookies are completely cool add the butter cream to a zip lock bag and cut a small piece of the tip off, pipe the buttercream on the bottom of one cookie and then take another cookie and place on top and slightly press down so it sticks and makes a sandwich. Repeat with all the other colors of cookies and then serve and enjoy!