Preheat oven to 350 degrees. In a large bowl, combine butter and sugars. Using a stiff spatula, stir and paddle the ingredients until uniformly combined. Add egg and whisk rapidly until combined into butter mixture. In a small bowl, combine flour, baking power and a three-finger pinch of salt. Fold flour mixture, in a few batches, into butter mixture until completely incorporated. In a small, shallow bowl, stir together ingredients for the spiced sugar until spice is uniformly distributed into sugar. Scoop out tablespoons of the dough, roll them in the spiced sugar and place them about 3 inches apart on a baking sheet. If you want them uniform, press each one down with a flat-bottomed pint glass or measuring cup. Bake until cooked through and edges are golden, about 15 min. Sprinkle with more sugar as they cool, if desired.
Make a few batches each rolled in a different flavored spiced sugar for an impressive holiday cookie exchange treat.