• If you're making cookie press/spritz cookies, preheat your oven to 350°F and set out large, very clean rimmed baking sheets and leave them unlined.
• In the bowl of a food processor fitted with the steel blade, place the flour, xanthan gum, sugar, and salt.
• Chop the butter into 6 to 8 large pieces and scatter on top of the dry ingredients, then add the egg yolks, and vanilla.
• Process until the dough until it's very smooth. It will first clump into a ball, and then stick to the sides of the machine's bowl. Don't overprocess which can heat up and begin to melt the dough (it should take 3 minutes or less).
• It should be smooth and a bit wet, but you should be able to handle it lightly with your hands without its sticking.

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. Place the press perpendicular to the baking sheet firmly, and press down the level for one “click” of the press per cookie. Hold the press steady on the surface for a moment to let the dough to adhere, then release quickly in a swift upward motion.
• If the cookies seem at all greasy, chill the shapes in the refrigerator just until they're mostly firm to the touch (about 10 minutes).

For icebox cookies

• Set out rimmed baking sheets and line them with parchment paper.
• Shape the cookie dough into a cylinder about 8-inches long, and place on a sheet of parchment paper. Roll the dough up in the paper, then square each of the sides with a straight edge like a bench scraper to form a rectangle that's about 8-inches long x 2-inches wide. Place the log in the refrigerator until just firm enough to slice (about 30 minutes).
• While the cookie dough is chilling, preheat your oven to 350°F.
• Remove the log from the freezer, unwrap it, smooth and square the edges again if necessary, then use a large, sharp knife to slice it by cross-section into pieces about 1/4 inch wide. Place the cookies about 1-inch apart on the prepared baking sheets, evenly spaced.

For both types of cookies

• With a pastry brush, brush the tops of all of the raw shaped 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 your icebox cookies to cool completely on the baking sheet.

For spritz cookies (special cooling instructions)

• If your spritz cookies have been coated with egg white before baking, allow them to cool for 5 minutes only. Run the 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.