Preheat the oven to 350°F and prepare a 9-by-9-inch (23 × 23 cm) baking pan with a sheet of parchment to fit the bottom. Butter the sides of the pan. Reserve.
Break the baking chocolate into chunks and cut the butter into pieces. Melt together the butter and chocolate, either in a double boiler or (in a nonmetallic bowl) in the microwave in 30-second increments, stirring in between sessions. Heat until smooth and creamy.
In a large bowl, whisk together the eggs, sugar, vanilla extract, and salt.
Place 1/3 cup (80 ml) of this mixture in a separate bowl, add the tahini and 1 tablespoon (8 g) of flour, and stir to combine. This will be the “tahini batter.”
To the larger bowl of batter, add the melted chocolate and butter, stirring with a rubber spatula or large wooden spoon to combine. This will be the “chocolate batter.”
Add the rest of the flour and the cocoa powder to the chocolate batter and stir well.
Pour the chocolate batter into the prepared pan and spread with an offset spatula to smooth.
Using a spoon, dollop the tahini batter on top of the chocolate batter. Take a spoon, or long skewer, and slightly mix the two batters to create a marbling effect.
Bake in the oven on the middle rack at 350°F for 30–35 minutes, or until a toothpick comes out cleanly from the center.
Remove from the oven and place on a wire cooling rack.
Using a paper towel, add a few drops of gold food coloring and then rub onto the front of the peeled chocolate coins.
After the brownies have cooled for about 10 minutes, sink chocolate coins, evenly spaced, halfway into the top. The coins will soften slightly.
Let the brownies cool completely, then remove from the pan.
Cut into squares and plate, or store in a covered container until use.
