Preheat oven to 425 degrees.
Spray a 20-tin donut pan with cooking spray.
Set aside.
In a large mixing bowl, whisk flour, baking powder, baking soda, salt and granulated sugar.
Set aside.
In a medium sized mixing bowl, whisk the buttermilk, sour cream and eggs until smooth.
Whisk in melted butter, canola oil, vanilla extract and nutmeg.
Pour the butter mixture into the flour mixture.
Stir just until combined.
Do not overmix.
Batter will be very thick.
Spoon batter into a large zip-lock bag.
Trim a corner off the bottom of the bag and pipe batter into each donut cavity.
Fill each cup 3∕4 full.
Bake for 10 minutes at 425 degrees or until the edges are lightly browned.
Remove from oven and cool approximately 2 minutes on a cooling rack.
Remove donuts from the pan and place on cooling rack.
Spoon glaze over top of donuts and swirl with the back of the spoon until glaze totally covers the top of the donuts.
Place donuts on cooling rack and allow any excess icing to drip off donuts.
Allow donuts to rest on cooling rack approximately 10 minutes until icing sets.
Serve.