In a large bowl whisk together the melted butter, vegetable oil, and granulated sugar. Add the egg and vanilla extract whisking to combine.
Whisk Wet Ingredients
Next, add the buttermilk.
Mix Wet Ingredients
In a separate bowl combine the all-purpose flour, baking powder, salt, and chocolate chips.
Whisk Dry Ingredients
Add the dry ingredients to the wet ingredients gently folding. Do not over mix.
Using a large scoop divide the batter between 7-8 cups in the prepared muffin pan. Sprinkle demerara sugar on top.
Prepare to Bake
Bake for 5 min then reduce the temperature to 350F and bake for 10 to 13 minutes, or until a toothpick inserted comes out clean.