Step 1

Preheat oven to 350°F. Line two cookie sheet with silicone baking mats or parchment paper.

Step 2

Cream butter and sugar in the bowl of a stand mixer fitted with the paddle attachment (or a large bowl with a hand mixer). Cream until the mixture is fluffy, about one minute.

Step 3

Add the egg, egg yolk, and vanilla and mix until smooth, then mix in baking soda, cream of tartar, and salt. Add flour and mix until cookie dough forms.

Step 4

Scoop 2 tablespoon sized balls 2-inches apart on cookie sheet. Bake for 11-15 minutes, or until the bottoms are just starting get golden and the top is no longer glossy. Cool at least 10 minutes on cookie sheet before removing. Cool completely before frosting.

Step 5

Mix butter in a large bowl with a hand mixer until smooth, then slowly mix in the powdered sugar a bit at a time. The mixture will be very crumbly. Add the vanilla and mix, then mix in the salt and milk. Beat until smooth and creamy.

Step 6

Tint with food coloring, if desired.

Step 7

Frost cooled cookies. Store loosely covered.

Step 8

Scoop balls of cookie dough and roll them in sugar or cinnamon sugar before baking. Skip frosting. OR

Step 9

Add 1 cup of sprinkles to the dough before scooping. Skip frosting.