Preheat oven to 350 degrees F. Line 2 large baking sheets with parchment paper; set aside.
In a large bowl with an electric mixer, beat butter and both sugars until fluffy. Mix in egg and vanilla until well blended. Combine flour, cinnamon, baking soda, salt, baking powder and nutmeg in a bowl. Stir into butter mixture. Gently stir in oats until well blended.
Shape dough into rounded golfball-sized balls (about 2 Tbsp. each). Place on prepared baking sheet (I fit 9 per sheet). Flatten with the bottom of a measuring cup dipped in sugar.
Bake for 8-10 minutes. Let cool on baking sheet 5 minutes before removing to a wire rack to cool completely.
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