In a medium bowl, combine flour, baking powder, cream of tartar, salt, and baking soda. Whisk to combine.
In the bowl of an electric mixer, with the paddle attachment, beat the butter and sugar together until light yellow and fluffy in texture (about 3 minutes) add the egg, cake batter extract and vanilla extract and mix to combine.
Reduce the mixer speed to low and slowly add the dry ingredients. mix until combined. Fold in 1/4 cup of the rainbow sprinkles.
Put the remaining sprinkles, using more as necessary, in a small bowl. Using a cookie scoop, scoop 1.5 tbsp of dough into rounds and roll through rainbow sprinkles ensuring total coverage. Repeat with remaining dough.
Place cookies in freezer for about 15 minutes and preheat your oven to 350F
Prep two sheet pans with parchment paper and place cookies 2 inches apart. Bake until the cookies have spread, and are just golden around the edges (10-12 minutes depending on your oven) Let cool on the cookie sheet for 5 minutes before removing to a cooling rack and allowing to cool completely.
Store in an airtight container for up to 4 days. Enjoy!