Ingredients
1/2 cup unsalted butter, cut into pieces
4 ounces unsweetened chocolate, cut into small pieces
1 1/4 cups sugar 2 large eggs
1 teaspoon vanilla extract
1/4 cup tapioca starch
1/4 cup potato starch
1/8 teaspoon salt
1/2 cup bittersweet chocolate chips

Directions

• Preheat oven to 350 degrees F.
  
• Line an 8-inch square pan with aluminum foil (cover both bottom and sides).
  
• Grease the bottom of the foil with butter or nonstick spray
  
• Melt the butter in a medium saucepan.
  
• Add the chocolate pieces and stir constantly with a whisk over low heat until the chocolate melts.
  
• Remove from heat and stir in the sugar, add the eggs one at a time, and then add the vanilla.
  
• Stir in the flour and the salt.
  
• Stir the mixture vigorously until the batter is smooth, glossy, and beginning to come away from the sides of the pan.
  
• Stir in chocolate chips, if using. Scrape the batter into the prepared pan.
  
• Bake for 30 minutes, until the center is almost set.
• Set to cool.