Preheat oven to 350 degrees.

In a medium sized saucepan, add your butter, vegetable oil, and 1/3 of your sugar (1/2 cup). Put saucepan over medium-low heat for 1-3 minutes (or until butter is melted).

While the butter mixture is melting, combine the rest of your sugar (1 cup) and your eggs in a medium/large bowl or stand-mixer.

Slowly add your butter mixture to your bowl. Constantly stir your mixture, so the eggs don’t cook. (Do not beat the mixture. The more air bubbles in your mixture, the less fudgy it will be.)

Add in your dry ingredients (flour, espresso powder, baking powder, and cocoa powder) and mix with a spatula (to avoid adding air bubbles).

Add your chocolate chips

Pour batter into 9x9 square pan lined with parchment paper.

Make sure to rub butter on pan before putting on parchment paper to help it stick. You can clip down edges with black binder clips to keep parchment paper out of the way (they are oven safe!) (if you use other clips, make sure it is oven safe).

Put clumps of peanut butter and marshmallow fluff on top of brownies.

Use a utensil (I used a chopstick) to spread the marshmallow and peanut butter.

Put brownies in oven for 28-32 minutes at 350 degrees fahrenheit.

Let your brownies cool in the pan for about 10 minutes before putting in fridge (I put mine in the freezer) for about 5 minutes. You can skip this step, although it helps my brownies not get crumbly when I cut them!

Cut brownies with large knife or plastic knife (brownies don’t stick to plastic knives)

Store these in the fridge for up to 12 days or at room temperature for 10 days!