Buttermilk Doughnuts

2 1/4 cups all-purpose flour, plus more for dusting 

3/4 tsp. freshly grated nutmeg 

1/2 tsp. ground cinnamon 

1/2 tsp. baking powder 

1/2 tsp. baking soda  

1/2 tsp. salt 

1 egg 

1/2 cup granulated sugar 

1 Tbs. unsalted butter, melted 

1/2 cup buttermilk 

Peanut or canola oil for deep-frying 

Confectioners’ sugar for dusting