Heat oven to 350°F and arrange rack in the middle. Combine butter and sugar in the bowl of a stand mixer and beat on medium until light and fluffy, about 3 minutes. Creaming the butter and sugar together like this causes the sugar crystals to cut into the butter, creating pockets full of air which will give the cookies a light texture after baking, so don't skimp on this step.

Add yolks, vanilla, and salt and beat until smooth. Add flour, baking soda, and cream of tartar and mix on low until flour is fully incorporated. Scoop dough into tablespoon-sized balls. Roll dough in sugar to coat and place on parchment-lined baking sheets.

Bake for 15 minutes or until the bottoms are just beginning to brown, but cookies are still soft in the center. Immediately transfer to a wire rack to cool.