Add butter and sugar to a bowl, beat together with either a hand or stand mixer until light and fluffy, about 3 minutes. Add in the egg, milk, and vanilla extract, beat to combine.

In a separate small bowl, mix together the gluten-free flour, baking powder, and salt.

Add the flour mixture into the butter mixture and mix until a dough forms. Cover dough with plastic wrap and chill in the fridge for at least 1 hour and up to overnight.

When ready to bake, preheat your oven to 375° Fahrenheit and remove dough from fridge. Roll the dough on a lightly floured surface to about ¼-inch thick, then use a cookie cutter to cut the dough into shapes.

Place cookies on a baking sheet and bake for 7-10 minutes. Remove from oven and transfer to a wire cooling rack to cool completely before decorating.