For the brownies:

1. Preheat the oven to 350 degrees F and line a 9x9 inch square pan with parchment paper.
2. In a large bowl, add the chocolate, butter, tahini, brown sugar, and granulated sugar. Heat the mixture in the microwave in 20 second increments, stirring with a rubber spatula in between, until everything is fully melted.
3. Quickly whisk in the eggs and vanilla until fully combined.
4. Lastly, fold in the flour, cocoa powder, and salt until just combined.
5. Spread the batter into the prepared square pan and bake for 33-36 minutes.
6. Allow to cool completely in the pan before frosting.

For the chocolate tahini frosting:

1. In a medium glass bowl, add the chocolate and tahini, and place over a small saucepan with simmering water. Stir often until the chocolate is fully melted.
2. Remove the bowl from the double boiler, and gently stir in the sifted powdered sugar a little at a time.
3. Once all of the powdered sugar is mixed in, allow the frosting to sit for about 10 minutes to thicken.
4. Frost the cooled brownies and sprinkle with sesame seeds, as desired. Cut into 16 squares and enjoy!