Cream butter, shortening, and sugar with an electric hand mixer or stand mixer. Beat in eggs, molasses and root beer concentrate.
In a separate bowl whisk flour, cream of tartar, baking soda, and salt together.
Combine dry ingredients with butter mixture.
Scoop cookies, using a medium cookie scoop, then place on baking sheets lined with parchment paper (I usually bake 6 cookies per sheet).
Bake for 13 minutes.
Allow cookies to cool for 3-5 minutes before transferring to a cooling rack.
Root Beer Frosting
Beat frosting ingredients together. Spread over cooled cookies.
Video
Notes
Butter can be used instead of shortening, but may slightly affect the thickness or shape of the cookie.Store cookies in an airtight container, or covered in plastic, at room temperature. Cookies can also be chilled.