Preheat the oven to 350°F. Grease a 9x13 inch baking pan and set aside.
In a large bowl, mix together the melted butter, sugar, and vanilla.
Add the eggs, one at a time, mixing well after each addition.
In a separate bowl, whisk together the flour, cocoa powder, and salt. Slowly add the dry ingredients to the wet ingredients, stirring until just combined.
Add the espresso and mix until completely incorporated.
Pour half of the batter into the prepared pan. Sprinkle the chocolate chips over the batter. Pour the remaining batter over the chips and spread evenly.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Cool completely before cutting into bars.
Dust with powdered sugar, if desired.
Interesting Facts
Mocha is a combination of chocolate and coffee.
Brownies were first created in the United States in the late 1800s.
The perfect brownie should have a crispy crust and a soft, fudgy center.