Step 1

Prepare a large baking sheet with parchment paper and set aside.

Step 2

Combine the flour, baking powder, baking soda, cream of tartar, and salt in a medium bowl. Whisk together and set aside.

Step 3

Beat the butter and sugar together with an electric mixer until creamed, about 1 minute. Add the egg and vanilla and continue to mix until well combined.

Step 4

Gradually add the flour mixture to the butter mixture and mix on low until all ingredients are well combined. Dough will be sticky.

Step 5

Lightly wet your hands, then scoop about 2 tbsp of the dough and roll it into a ball and place it on the baking sheet. Continue until you have about 15 dough balls.

Step 6

Cover dough balls with plastic wrap and put them in your refrigerator for at least 2 hours or overnight. You can chill the dough up to 4 days in advance.

Step 7

Preheat the oven to 350°F and arrange the chilled cookie dough balls so they are 3 inches apart on the baking sheet. Depending on the size of your baking sheet, you may need to bake them in batches. They will spread and they need plenty of space between them. Bake for 11-12 minutes or until lightly browned on the sides but still soft in the center. Remove from the oven and allow the cookies to cool for 5 minutes before transferring them to a wire rack. Allow cookies to cool completely before frosting them.

Step 8

To prepare the frosting, beat together the Open Nature Buttercream frosting mix with softened butter and milk, as noted on the packaging, until you have a light and creamy frosting. Smear the frosting on each cookie with a butter knife and decorate the tops with decorating sugar or sprinkles. If you are not using the Open Nature Buttercream frosting mix, see Notes below for an alternative buttercream recipe.

Step 9

Refrigerate the cookies for 30 minutes to allow the frosting to set, and store uneaten cookies in a sealed container in your fridge for up to 5 days.