Preheat oven to 425 degrees. Lightly grease a mini muffin tin, or line with paper liners and grease the liners with non-stick cooking oil spray.
With an electric mixer, cream together the vegetable oil and sugars till smooth. Add the eggs, beating to combine.
Stir in the baking powder, baking soda, nutmeg, cinnamon, salt, and vanilla.
Stir the flour into the creamed mixture alternately with the buttermilk, beginning and ending with the flour.
Spoon the batter evenly into the prepared pan, filling the cups nearly full. Bake for 13-15 minutes or until muffins are a pale golden brown and a toothpick inserted into the middle of one of the center muffins comes out clean.
Remove muffins from oven and let them cool for five minutes on a wire rack. While they're cooling, melt the butter for the topping in the microwave. Stir together the cinnamon and sugar.
Dip the tops of muffins into the melted butter, then roll in the cinnamon-sugar.