Preheat oven to 425 and spray donut pan with baking spray.
Combine oil, granulated sugar, and butter in a large bowl. Add in vanilla extract and eggs. Mix well.
In a separate bowl, sift together the flour, baking powder, baking soda, salt, and nutmeg.
Pour half the flour mixture into the wet ingredient bowl. Mix to combine, and then add half the buttermilk. Pour in the rest of the flour mixture, and follow with the rest of the buttermilk. Mix until well combined.
Spoon the batter into a piping bag and fill the donut pan forms about 3/4 full. Bake 8-9 minutes. Remove from pan and onto a cooling rack with parchment paper underneath.
Combine the confectioner's sugar, vanilla extract, and milk in a bowl. Spoon over warm donuts and allow glaze to finish dripping down the sides before serving.