Preheat the oven to 350 degrees F. Line two large rimmed baking sheets with parchment paper. If using a convection oven, preheat to 330 degrees F.
Whisk together the flour, baking soda, cream of tartar and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter and both sugars on medium speed for about 2 minutes. Stop mixer, scrape the bowl and beat on medium high for another 2-3 minutes or until light and creamy.
Add the egg and beat for another minute, stopping to scrape the side of the bowl after 30 seconds. Beat in the flavorings (vanilla, almond and butter flavoring, if using)
Add the flour mixture, stirring just until it’s incorporated. The dough should be soft and scoopable.
Using a large cookie scoop, scoop 8 balls of dough onto a dinner plate. Shape them into balls then press down slightly to make ¾ to 1 inch thick rounds.
Cover tops with sparkly sugar.
Bake the cookies for about 15 minutes, rotating the pan halfway through, or until the cookies are lightly brown around the edges and the center appears set but is still a bit pale. It should have tons of little wrinkles and crevices.
Let cookies cool directly on the cookie sheet for about 10 minutes or until they are firm enough to stay on a rack without falling through. Transfer to a rack and let cool completely.