To make cookie dough, in the bowl of an electric mixer fitted with the paddle attachment, cream the butter and sugar together on high speed until light and fluffy. Add the egg and any flavorings and mix on medium speed to incorporate. Add the flour and mix on low speed until the dough comes together.
Roll between 2 pieces of plastic wrap and refrigerate for 30 minutes. In the meantime, preheat your oven to 350 degrees F. Cut out your cookies and place them on baking sheets.
Bake for 8 minutes or until the edges start to turn golden.
To make royal icing, place all 3 ingredients in the bowl of an electric mixer fitted with the whisk attachment. Mix on slow for a minute to combine your ingredients. Turn the mixer to high speed and mix for 7 minutes. Divide the royal icing in 6 parts to make each of the following colors: yellow, orange, red, blue, purple, green.
Recipe by Sweet Explorations at http://sweetexplorations.com/tetris-cookies/