Prep time: 10 minutes
Total time: 1 hour
12 tablespoons unsalted butter, diced, plus more for greasing
5 ounces|125 grams semisweet chocolate, chopped
1/2 cup plus 2 tablespoons dark chocolate chips
1/2 cup plus 2 tablespoons all-purpose flour
6 tablespoons unsweetened cocoa powder
1 teaspoon ground cinnamon
1 teaspoon kosher salt
3 large eggs
1 1/4 cup granulated sugar
1 teaspoon vanilla extract
2 teaspoons coarse sea salt
1 teaspoon coarse sugar
1. Heat the oven to 350°F. Grease and line a 9-inch-by-13-inch baking pan with parchment paper. Grease the parchment paper again.
2. Fill a medium saucepan with about 2 inches of water over medium heat. Place a heatproof bowl over the top and add in the 12 tablespoons of butter, the semisweet chocolate, and 2 tablespoons of dark chocolate. Cook, stirring occasionally, until the butter and chocolate have melted. Remove from the heat and cool slightly.
3. In a medium bowl, whisk together the flour, cocoa powder, cinnamon, and kosher salt.
4. In a separate medium bowl, whisk together the granulated sugar, vanilla, and eggs. Beat the melted chocolate mixture into the wet ingredients, then add in the dry ingredients, mixing well to combine. Stir in the remaining 1/2 cup of dark chocolate chips, then pour the batter evenly into the prepared pan. Sprinkle evenly with the coarse salt and coarse sugar and bake until a toothpick inserted comes out clean, about 25 to 30 minutes. Cool completely, then cut into squares before serving.