Begin by making the cinnamon sugar chips to add to the batter. Stir together the melted butter, brown sugar, and ground cinnamon. Spread out into an even layer on a small pan lined with wax paper or parchment paper. Place the pan in the freezer for at least 15 minutes to solidify.

Preheat the oven to 400℉. Prepare muffin tins with parchment paper muffin liners or spray with non-stick spray

In a mixing bowl, whisk together the melted butter, oil, white sugar, and brown sugar. Add the eggs, vanilla, sour cream, and milk, and continue whisking until smooth.

In a separate bowl, whisk together the flour, baking powder, and salt. Add to the bowl of combined wet ingredients and whisk just until no streaks of flour remain.

Chop the chilled cinnamon sugar mixture into small pieces and gently fold into the muffin batter. (Reserve a little bit of the cinnamon chips for topping the muffins.) Distribute the batter evenly between 15 muffin liners, filling each liner almost to the top with batter. Crumble the reserved cinnamon chips on top.

Bake, one pan at a time, in a 400℉ oven for 5 minutes before reducing the temperature to 350℉ for another 10-12 minutes or until a toothpick inserted into the center comes out clean.