Line a metal 9x13 baking pan with parchment paper (or butter the bottom and sides) and set it aside. Preheat the oven to 350 F/180 C.
Cook the butter in a stainless steel pan over medium heat for 10-12 minutes or until browned. You’ll know it’s done when the top of the pan is covered in foam and there are brown bits of butter solid at the bottom of the pan. Pour the butter into your mixing bowl and set it aside to cool to room temperature.
Whisk the oil, brown sugar, and granulated sugar into the brown butter until well combined.
Whisk in the vanilla, eggs, and pumpkin.
Whisk in the flour, pumpkin spice, salt, baking powder, baking soda, and mini chocolate chips.
Pour the pumpkin cake batter into the prepared baking pan and sprinkle more mini chocolate chips over the top. Bake for 25-30 minutes or until a toothpick inserted into the center comes out covered in a few moist crumbs. Let it cool completely on a wire rack then cut into slices and enjoy!
Store leftovers in an airtight container or in the baking pan wrapped tightly in plastic wrap for 4-5 days. You can also keep it in the fridge and it will stay fresh longer. To freeze, wrap tightly in plastic wrap and store in an airtight container or freezer bag for up to 1 month.