Make the sugar cookie dough: Make 1 recipe sand tart cookie dough. Make the dough into a log shape and wrap it with food wrap, so that the dough doesn't dry out. Chill the dough overnight.
Stamp the cookies: Over a floured surface, slice the chilled dough into 1/4-inch slices, roll the dough, and stamp the dough with the cookie stamp, remove the excess dough.
Make the egg wash: In a small bowl, combine 1 large egg and 1 tablespoon of water, and whisk together. Brush egg wash over the tops of the cookies and optionally, sprinkle with sprinkles.