In a large bowl of a stand mixer, beat the room temperature butter and sugar together for about 30 seconds.
Then add the egg and mix until thoroughly combined. Add all the remaining ingredients except for the flour and mix again. Now add the flour gradually, and on a slow speed so you don’t have a flour flying all over the kitchen.
Divide dough into approximate thirds (dough will be very soft and wet), sandwich each third between wax paper or plastic wrap, roll or press into discs about 1/2” thick and chill for at least 30-60 minutes (overnight will work too).
Remove wax paper and roll dough out onto a lightly floured surface to 1/8” or slightly thicker and cut into desired shapes.
Place on sheet pans lined with silpat baking mats, or parchment paper and chill in the refrigerator for 8-10 minutes.
Bake for 6-8 minutes or until edge are set. Cool on wire rack. Decorate with royal icing.
Royal Icing
Mix all royal icing ingredients together except the last 2 tablespoons of water. Check consistency before adding the rest. You want thin, but not watery. If it gets too thin, add more powdered sugar. If it gets too thick, add more water. Add food coloring (I prefer gel colors because they are brighter, more intense and less watery.)