Preheat oven to 350F. Butter and line with parchment paper a 8x8" baking pan.

Add a single layer of the graham crackers to the prepared baking pan.

Fill a saucepan with 2" of water. Place over medium heat and bring to a boil.

In a large bowl, combine the butter and chocolate chips. Place the bowl over the saucepan and stir with a spatula until fully melted.

Remove the bowl from the heat and vigorously whisk in the sugars, eggs, yolk, and vanilla for 1 minute.

In a separate bowl, combine the flour, cocoa powder, (optional) espresso powder, salt, and baking soda. Mix well.

Add the flour mixture and chopped chocolate to the butter mixture. Fold all together with a spatula.

Transfer the brownie batter to the prepared pan.

Bake for 25 minutes.

Let cool in the pan 1-2 hours before slicing.