Preheat your oven to 350℉. Spray an 8x8 metal pan with nonstick spray and line with parchment paper.
Add cubed butter to a medium saucepan over medium heat. Melt the butter, stirring occasionally. Once it's melted, turn the heat to medium-low, and continue cooking the butter, stirring frequently until it turns a deep golden shade with a nutty aroma.
Once the butter is browned, remove the pot from the heat and immediately stir in your semi-sweet chocolate until completely melted, then whisk in the vegetable oil and cocoa powder. Set aside to cool slightly.
In a large mixing bowl, add the eggs, egg yolk, and granulated sugar. Whisk for about 1-2 minutes, until the sugar is fully dissolved.
Next, whisk in the powdered sugar, vanilla, and salt.
Check that the chocolate mixture is no longer piping hot and whisk it into the bowl of eggs/sugar. Fold in the flour & espresso powder, then the chocolate chips.
Pour the batter into your prepared pan, and bake for 29 to 32 minutes. The center will have the slightest wobble when you move the pan, and the outer edges will appear set.
Let the brownies cool in the pan on a wire rack for about 1 hour & 20 minutes before slicing and enjoying.
