Ingredients:
- 3 sticks plus 2 tablespoons unsalted butter
- 12 ounces best-quality bittersweet chocolate
- 6 eggs
- 1 3/4 cups superfine sugar
- 1 tablespoon pure vanilla extract
- 1 1/2 cups plus 2 tablespoons all-purpose flour
- 1 teaspoon salt
- 1/2 cup white chocolate buttons, chips, or morsels
- 1/2 cup semisweet chocolate buttons, chips or morsels
- Approximately 2 teaspoons confectioners' sugar, for garnish
- Special equipment: Baking tin (approximately 11 1/4 inches by 9 inches by 2 inches), sides and base lined with baking parchment.