Preheat the oven to 350 degrees F. Grease a mini muffin pan with softened butter.

In a small bowl, add the chocolate and oil. Place over a small saucepan of simmering water, and stir often until fully melted. Set aside to cool.

In a large bowl, add the sugars, eggs, and vanilla. Using an electric mixer, beat on high speed for about 5-6 minutes until the mixture has doubled in size.

While mixing on low speed, slowly pour in the chocolate oil mixture.

Once it is fully combined, add the flour, cocoa powders, espresso powder, and salt, and mix until mostly combined.

Fold in the chopped chocolate until evenly dispersed.

Add the brownie batter to the prepared mini muffin pan, filling each cup about ? full.

Bake the brownie bites for about 15-18 minutes or until a toothpick inserted comes out with a few moist crumbs.

Allow them to cool for a few minutes in the pan before removing. Repeat with the remaining brownie batter.