Preheat the oven to 425℉/218℃. Line a muffin tin with liners and set aside.
In a pot over medium-high heat, add the butter. Allow it to melt, then it'll begin to sizzle and foam. Continue stirring for 2-3 minutes until brown specks form on the bottom of the pot and the aroma of browned butter arrives. This should take 3-5 minutes total. Transfer to a heat-safe glass cup to cool as you prep the rest of the ingredients. The butter should sit and cool for 20 minutes before using.
1/2 cup + 2 tbsp unsalted butter
In a bowl, add the flour, baking soda, baking powder, cinnamon, cornstarch, and salt. Stir to combine and set aside.
2 1/2 cups all-purpose flour, 1 tsp baking soda, 2 tsp baking powder, 1/4 tsp cinnamon, 1 tbsp cornstarch, 1/4 tsp salt
In another large bowl, add the brown butter, oil, white sugar, buttermilk, eggs, and vanilla. Whisk well to combine (1-2 minutes).
1/3 cup oil, 2 large eggs, 1 cup white sugar, 2 tsps vanilla, 1 cup buttermilk, 1/2 cup + 2 tbsp unsalted butter
Combine the dry and wet ingredients together until almost fully combined. Then mix in the mini chocolate chips a few times.
Scoop evenly between the liners, filling them to the top. Sprinkle extra chocolate chips on top if desired.
3/4 cups mini chocolate chips
Bake for 7 minutes at 425℉, then lower the oven temperature to 375℉/190℃ (Don't open the oven door) and continue baking for another 12-15 minutes or until a toothpick inserted in the middle comes out clean.
Allow the muffins to cool, and enjoy!