Preheat oven to 350° F. Lightly grease a standard muffin tin with cooking spray, or using a pastry brush, coat muffin cups with vegetable oil.
In medium bowl, whisk together flour, unsweetened cocoa powder, baking powder, salt, nutmeg, and cinnamon. In a large bowl, using an electric mixer, beat together sugar and egg on medium-high speed until light in color, approximately, 15 to 20 seconds. Add the flour mixture to the sugar mixture in three batches, beating well after each addition. The final result will be unappealingly dry and hairy.
Add the vegetable oil, milk, cream and vanilla extract, beating until just combined---be sure not to over-beat the mixture.
Divide the batter evenly into the muffin tins, filling each about 3/4 full. Bake for 15-20 minutes, until a tester inserted in the center comes out clean.
While muffins are baking, melt butter over low heat in a small saucepan, and pour remaining sugar into a small bowl. Let muffins cool slightly in the pan for a minute, then carefully remove and place on wire rack.
Lightly brush the top, sides and bottom of each muffin with melted butter and roll in sugar. Cool completely on a wire rack.
Makes 12 Donut Muffins.