In a mixing bowl, cream butter and sugars. Add egg; mix well.
Combine the flour, cornmeal, baking powder, salt, and nutmeg; add to the creamed mixture alternately with milk just until moistened.
Fold in blueberries.
Coat muffin cups with nonstick cooking spray or use paper liners; fill two-thirds full with batter.
Bake at 400F for 18-22 minutes or until a toothpick comes out clean.
Cool for 5 minutes before removing from pan to a wire rack.