• Preheat your oven to 350°F. Set out large, very clean rimmed baking sheets, but don’t line any that you plan to use for spritz cookies. Line with unbleached parchment paper any baking sheets you plan to use for icebox cookies.
• In the bowl of a food processor fitted with the steel blade, place the flour, xanthan gum, sugar, salt, butter, egg yolks, and vanilla, and process until the dough comes together in a ball.
• It should be smooth and a bit wet, but you should be able to handle it lightly with your hands without its sticking.
• You can easily make these cookies without a food processor, although the dough will not be as uniform in color. Simply place the dough in a plastic bag and knead it with your hands until the color is as uniform as possible.

For spritz cookies.

• Do not chill the dough. Fill your cookie press according to the manufacturer’s directions.
• Place the disk you like on the end of the chamber, and screw the end on securely.
• On a bare, ungreased baking sheet that is not nonstick, dispense the cookie dough, spacing it evenly. Remember to place the press firmly onto the baking sheet, use one “click” of the press per cookie, hold the press steady on the surface for a moment to allow the dough to adhere to the sheet, and then release quickly in a swift upward motion.
• Place the baking sheet in the refrigerator or freezer to chill the dough until it’s firm to the touch.

For icebox cookies.

• Shape the cookie dough into a cylinder about 1 1/2 inches in diameter, and place on a sheet of unbleached parchment paper. Square each of the sides with a straight edge to form a rectangle, and place the log in the freezer until firm (about 15 minutes).
• Remove the log from the freezer, unwrap it, square the edges again if necessary, then slice it by cross-section into pieces about 1/4 inch wide. Place the cookies on a nonstick baking sheet, evenly spaced.
• For both shapes of cookies.
• With a pastry brush, brush the tops of all of the cookies on the baking sheet with the (optional) egg white, and sprinkle with the (optional) coarse sugar.
• Place the baking sheets, one at a time, in the center of the preheated oven and bake until they’re lightly brown around the edges (8 to 10 minutes).
• For slightly crispier cookies, allow them to brown a bit longer (up to 12 minutes total).
• Remove the baking sheet from the oven and allow the cookies to cool completely on the baking sheet.
• If making spritz cookies that have been coated with egg white before baking, allow the cookies to cool for 5 minutes (no more!) and run a edge of a small offset spatula or knife under the cookies to pry them from the baking sheet.
• Then, allow the cookies to finish cooling completely on the baking sheet before moving them.