Preheat the oven to 175 Degrees Celsius/ 350 Degrees Fahrenheit.

Add butter and oil to the saucepan, place it over medium heat and let it melt. Once the butter melts completely, turn off the heat and add powdered sugar + cocoa and whisk till combined for about a minute.

Add eggs + vanilla and stir only until the egg mix well, but do not overmix.

Finally, add the all-purpose flour + salt and mix until combined. Again, do not overmix.

Pour it into an 8*8 inch square pan lined with parchment paper or baking paper.

Tap the pan on the counter 2-3 times to get rid of bubbles, if any.

Bake for about 25-30 minutes. I bake mine when the center is slightly wet and chewy. If you want it set, then let it cook for additional 5 minutes.