Preheat oven to 400 degrees. Adjust oven racks to upper middle and lower middle racks.

In a bowl, stir to combine flour, cream of tartar, baking soda, nutmeg and ground cinnamon. Set aside. In a stand mixer with a paddle attachment set on medium speed, add in softened butter and sugar beating until smooth. Add in eggs one at a time, beating for 30 seconds in between additions. Add in rum extract. With mixer speed set on low, add in dry ingredients mixture until just combined.

In small bowl, whisk together snickerdoodle coating ingredients. Roll about 1 Tablespoon of dough into ball. Roll the dough ball into the snickerdoodle coating mix until the dough ball is evenly coated. Place on a parchment lined baking sheet. Repeat until two baking sheets are full.

Place baking sheets in the oven and bake for 4-5 minutes. Remove cookie sheets, rotate and switch the sheets to the opposite baking rack. Bake an additional 4-5 minutes. Remove from oven, and allow the cookies to cool on the sheet for 5 minutes before removing them to a wire rack to finish cooling. Serve when cool.