Preheat the oven to 350 F. Line a 9x13 pan with parchment paper.
Heat milk and butter in a microwaveable-safe mixing bowl for 1-2 minutes, till butter is melted and milk is hot.
Add cocoa powder and oil to the hot milk and melted butter and stir till well combined.
Mix in eggs and egg yolks.
Stir in sugar.
Add in flour, salt, and espresso powder until combined.
If using chocolate chips, stir in now.
Pour the mixture into the lined pan and bake for 30 minutes. The brownies will seem undercooked.
Let cool completely (uncovered overnight if possible) and cut into squares. Enjoy!