Preheat the oven to 425ºF (218ºC). Spray the wells of a 6-count jumbo muffin tin (or line with jumbo liners) generously with non-stick spray. Set aside.

In a medium size bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large bowl, whisk together the cooled butter, vegetable oil, granulated sugar, and brown sugar until the mixture is smooth. Add the eggs, vanilla, and buttermilk and whisk again until everything is thoroughly combined.

Gently fold the dry ingredients into the wet ingredients. When the batter is mostly combined, add the chocolate chips and continue stirring gently until everything is incorporated, being careful not to overmix. Allow the muffin batter to rest for 15-20 minutes (you do not need to cover it).

After the batter has rested, spoon the batter evenly into the 6 wells. Two ice cream scoops full works best, totaling about ½ cup of batter in each well. Sprinkle with additional chocolate chips and sanding sugar.

Bake the muffins for 7 minutes, then reduce the oven temperature to 350ºF (177ºC) without opening the door, and bake for another 20-22 minutes. Muffins are done when a toothpick inserted into the center comes out mostly clean and the tops are golden brown. Remove from the oven and allow them to cool in the pan for no more than 10 minutes before removing from the pan to cool completely on a wire rack.