Preheat the oven to 350° Fahrenheit.
Line an 8x8 pan with parchment paper. Removal will be easiest if you line it going both ways. In a mixing bowl, whisk together all wet ingredients until smooth.
Add in the dry ingredients, aside from the chocolate chips. The batter will be fairly thick.
Fold in the chocolate chips if using. Spread evenly into the lined pan.
Whisk together the tahini and powdered sugar. Make dollops on top of the brownies, then use a toothpick to create swirls.
Bake for 25-30 minutes or until a toothpick comes out mostly clean. If you prefer really fudgy brownies, bake for closer to 25 minutes, if you prefer them more well done, bake for closer to 30.
Let cool completely, then slice and enjoy!