Using the paddle attachment of a stand mixer, cream the butter until light and fluffy, about 3 minutes.

Add in the powdered sugar, salt, and vanilla extract and mix until combined.

Mix in the flour until well combined, scraping down the sides as you go.

Transfer the dough onto a sheet of parchment paper and shape into a rectangular prism. Alternatively, you could roll out the dough and cut equally sized rectangles. The second method will give you a little more consistency in cookie thickness!

Refrigerate the dough for 30 minutes while the oven preheats.

Place the cookies on a lined baking sheet, ½ inch apart.

Bake for 10 minutes at 350°F, or until the edges of the cookie are golden brown but the tops are still light.

Allow to cool fully before icing.

Divide the icing between 6 different bowls and add your preferred gel food coloring.

Add ¼ cup of each color to a shallow dish, allowing the colors to swirl together.

Dip each cookie in the icing, allowing the excess to drip off before transferring to a wire rack to set fully.

Allow the cookies to set for 6 hours before eating or packaging!