Prepare the Dough: In a large mixing bowl, blend the ground almonds, powdered sugar, salt, and cinnamon. In a separate bowl, whisk the egg whites until foamy (or soft peaks if using a stand mixer). Add the almond liqueur (or almond extract with water) to the egg whites.
Combine: Add the egg white mixture to the dry ingredients and knead until well combined. Wrap the dough in cling wrap and refrigerate overnight to allow the flavors to develop.
Make the Glaze: In a bowl, beat the egg white while gradually adding the powdered sugar until smooth.
Roll the Dough: Sprinkle powdered sugar on your work surface. Take one-quarter of the dough at a time and roll it out to ¼-inch thickness.
Cut and Frost the Cookies:
Method 1: Use a floured or wet star-shaped cookie cutter to cut out stars. Place them on parchment-lined baking sheets. Spread or brush the glaze evenly over the stars, then refrigerate for 1-2 hours before baking.
Method 2: Spread a thick layer of icing evenly over the entire sheet of dough. Freeze for 2 hours before cutting out the stars and baking.
Bake the Cookies: Preheat the oven to 275°F (135°C). Bake the cookies on a parchment-lined baking sheet for 12-15 minutes until they are set but not browned. Allow the cookies to cool on the baking sheets for 5-10 minutes before transferring them to wire racks to cool completely.