Preheat oven to 375 (for big muffins 350 for 40-45 minutes)

Mix sugar, oil, egg, milk, and vanilla well

Stir in sour cream

Stir baking powder, cocoa powder, and flour in until just combined

Fold in chocolate

Scoop batter into a muffin tin or silicone muffin cups

Bake for 20-25 minutes

Makes 8-12 muffins (depending on how much batter you put in each cup)