Preheat oven to 350 F. Line a cake pan with parchment paper, and set aside.
In a large bowl, mix together the tahini, eggs, maple syrup, and vanilla until smooth.
Add the coconut sugar, cocoa powder, espresso powder (optional), baking soda, salt. Mix everything together.
Then, mix in the chocolate chips. The batter will be thick. Because there is no flour, don’t worry about over-mixing the batter.
Pour the batter into the cake pan, and spread the batter so it's flat.
Transfer the pan to the oven, and bake for about 30 minutes, until the brownie is puffed and the top is firm to the touch.
Cool the brownie on a wire rack at room temperature until completely cool (about 1 hour).
Then, transfer to the freezer for 30 minutes to harden.