The idea behind these adorable paintbrush cookies is to cut them with holiday-themed cookie cutters then decorate them with festive colors and sprinkles.
In a large bowl of the stand mixer add powdered sugar, butter, vanilla, almond extract and egg. Beat on low with a paddle attachment.
Add the flour, baking soda, and cream of tartar. Mix until well combined. Cover and refrigerate 2 to 3 hours.
Heat oven to 375°F. Lightly grease cookie sheet with shortening or spray with cooking spray. On a lightly floured surface, roll dough 3/16 inch thick. Use the cookie cutters to make designs. Place on the baking sheet about 2 inches apart.
In a small bowl, mix the egg yolk and water. Divide mixture among several smaller bowls. Tint each with a different food color to make bright colors. (If paint thickens while standing, stir in a few drops of water.) Paint designs on cookies with small paintbrushes and embellish with sprinkles.
Bake 7 to 8 minutes or until edges are light brown. Remove from cookie sheet to wire rack to cool.
Notes
I suggest using gel food coloring over the liquid kind as the colors will be much more vibrant.