Step 1: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper to prevent sticking.
Step 2: In a large mixing bowl, combine the almond flour, whey protein powder, and powdered sweetener. If using salt, add it here as well. Whisk until well blended.
Step 3: Add the cold, cubed butter to the dry ingredients. Use a pastry cutter or your fingers to work the butter into the flour mixture until it resembles coarse crumbs.
Step 4: Create a well in the center and add the egg yolk and vanilla extract. Mix until the dough begins to come together.
Step 5: Take small portions of the dough and roll them into crescent shapes, about 1 inch wide and 2-3 inches long. Place on the prepared baking sheet, leaving space between each cookie.
Step 6: Bake the cookies for 12-15 minutes or until lightly golden on the edges. Keep an eye on them, as baking times may vary.
Step 7: Once baked, allow the cookies to cool on the baking sheet for a few minutes. Transfer to a wire rack to cool completely. Dust with additional powdered sweetener before serving.