Preheat the oven to 350 degrees.
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.