In a medium bowl, whisk together all dry ingredients (except sugar substitute) until well combined, set aside.
In a separate bowl - the bowl of a stand mixer fixed with a paddle attachment, or a large mixing bowl, if using a hand mixer - cream softened butter and sugar substitute until smooth and fluffy.
Be sure to scrape down the sides of the bowl a few times, to make sure everything is incorporated into the mix.
Add the eggs and vanilla extract to the mix, beating well to combine.
With mixer turned down to low speed, slowly add dry ingredients mix to the mixing bowl of wet ingredients, and carefully mix until well incorporated and a smooth dough forms.
Wrap dough ball in plastic film, chill for 1 hour. This is an important step for any gluten free cookie dough, don’t skip it!
Line 2 cookie sheets with pieces of parchment paper.
Lightly dust work surface with a little more protein powder, roll dough out to about ¼″ thick (can be slightly thicker).
Use cookie cutters to cut out whatever shapes you’d like, place cookies 2″ apart on prepared cookie sheets. Cover and chill for 30 minutes.
Preheat oven to 350 F.
Bake cookies for 8-10 minutes, or until golden brown on the bottom. . Keep an eye on them - smaller cookies will be done faster than larger ones will be.
As they come out of the oven, transfer each cookie sheet to a wire rack to start cooling. After 5 minutes, cookies can be removed from the pan and allowed to cool on their own.
Note: The secret to perfectly flat cookies for decorating is to place a clean baking sheet over the pan of freshly baked cookies, as soon as they’re taken from the oven. Gently press down, only enough to level them.
Once cooled to room temperature, store your low carb sugar cookies in an airtight container until decorating or serving.A freezer bag works well for undecorated sugar cookies, but once decorated, they should be stored in a single layer, to keep the decorating intact.