Dough: Cream together butter, shortening, and 1 1/2 cups sugar. Add eggs and vanilla and mix well. Add the flour, cream of tartar, baking soda and salt and stir until combined.
Chill dough for at least 30 minutes, if possible (or up to 3 days).
Shape dough by heaping tablespoonfuls into balls, to make about 24 cookies.
Cinnamon sugar: In a separate bowl, mix the 4 tablespoons granulated sugar and the cinnamon. Roll balls of dough in mixture. Place dough about 2 inches apart on a parchment lined baking sheet.
Bake 8 to 10 minutes (don't over bake!). Allow to cool for a few minutes on the baking sheet before remove to a cooling rack to cool completely.
Video
Notes
Shortening: you may use all butter for this recipe! The shortening just helps make them extra soft and tender.Storing Instructions: Keep leftover cookies in an airtight container at room temperature for up to 3 days.Freezing Instructions: Let snickerdoodle cookies cool completely then transfer to a freezer safe bag and place in the freezer for up to 3 months.