Preheat the oven to 350 degrees F. Line an 8-inch square baking pan with 2 overlapping sheets of parchment paper.

In a small bowl, stir together the cornstarch and cocoa powder until fully combined. In a small saucepan over low heat, melt the chocolate, coconut oil and 1 tablespoon tahini, stirring until smooth.

In a large bowl, beat the eggs, granulated sugar and brown sugar on medium-high speed until smooth and doubled in volume, about 3-4 minutes. Mix in the salt and vanilla followed by the chocolate mixture until fully combined. Add the cornstarch, beating on low. Once combined, beat on medium high-speed until the batter thickens, about 30 seconds.

In a small bowl, combine the remaining tahini and agave syrup. Transfer the batter to the prepared baking pan smoothing into an even layer. Dot the top of the batter with the tahini-agave mixture. Use a toothpick to swirl. Bake for 20-25 minutes until a toothpick inserted in the center of the brownies comes out with only a few crumbs. Cool before taking the brownies out of the pan and cutting into 16 squares.

Store in an airtight container.