In a bowl, mix the cooled milk, melted butter, vegetable oil, sour cream, eggs, and vanilla extract.
In another bowl, whisk together the flour, baking powder, baking soda, salt, and sugar.
Combine the wet and dry ingredients, mixing until just combined—don’t overmix!
Fill the muffin tins about 3/4 full with batter and sprinkle with coarse sugar.