Preheat oven to 350℉. Line an 8x8 baking dish with parchment paper. Set aside.

In a small bowl, whisk the cornstarch and cocoa until smooth and no lumps are visible.

Using a small saucepan, heat the chocolate, oil, and 1 tablespoon of tahini over medium low heat stirring constantly. Once smooth, remove from heat.

With an electric mixer, beat the eggs and sugar until light and smooth for approx. 4-5 minutes on med-high speed. Reduce speed to medium and beat in the salt and vanilla.

Pour in the chocolate mixture and mix until incorporated well.

Add the cornstarch mixture and increase speed back to med-high and beat until batter seems a bit stiff, will only take about a minute.

Transfer to prepared baking dish and smooth out batter evenly into dish.

In a small bowl, combine agave and remaining 3 tablespoons tahini. Place about 5-6 dollops of tahini mixture onto batter. Swirl tahini into batter with a toothpick or skewer.

Bake for 24-28 minutes. Edges will puff up a bit and when a toothpick inserted comes out with only a few moist crumbs.

Let cool and then remove from pan and cut into squares.