Have oven racks at upper middle and lower middle.
Preheat oven to 400°
Line cookie sheets with parchment paper or silicone mats
Grate nutmeg
Whisk together the flour, cream of tartar, nutmeg, and baking soda. Set aside.
In a stand mixer with the paddle attached beat the butter and sugar until light and fluffy. About 3 to 5 minutes.
Add eggs one at a time being sure to mix well after each one.
Add in rum or rum extract and mix well.
Reduce speed to low and add flour mixture. Mix until just combined.
Roll 1 TBS of dough at a time into balls (I use a cookie scoop) and place them 2 inches apart on the prepared cookie sheets.
Press dough balls
Grease the bottom of a drinking glass or measuring cup (I used cooking spray) and press the dough balls down evenly to an even 1/2 inch thickness.
Bake until the edges are lightly browned, 8 to 10 minutes.
Switch and rotate the sheets halfway through baking.
Let the cookies cool on the sheets for 5 minutes then remove them to wire racks to cool completely.
Dust with confectioners' sugar.