• Preheat the oven to 350°F. Lightly coat a 9x13-inch pan with nonstick spray or line with parchment paper. Set aside.
• Create a double boiler by adding a small amount of water to a small saucepan, then setting a metal bowl over the top. Heat to boiling, then reduce to a simmer. Cut the butter into pieces and break apart the chocolate and add both to the bowl. Melt, stirring often, until completely smooth. Remove from heat and set aside.
  9 1/2 ounces unsalted butter, 5 1/2 ounces 60% bittersweet chocolate
• In a large mixing bowl, stir together sugar, flour, baking powder, and salt. Pour in the melted chocolate mixture and stir to mix. Continue to stir for about 5 minutes; the mixture will become thick, almost like a dough. This will help blend everything well and cool the chocolate.
  1 1/2 cups granulated sugar, 3/4 cup all-purpose flour, 1/8 teaspoon baking powder, Pinch fine sea salt
• Stir in the eggs one at a time, making sure they are fully mixed before adding the next. The batter should now look smooth and silky.
  5 large eggs
• Pour into the prepared pan and spread to the edges and corners. Scatter the chopped walnuts over the top in a single layer, pressing gently into the batter.
  1 1/2 cups chopped walnuts
• Bake for 30 minutes, until slightly risen and edges are starting to pull away from the pan. Do not overbake. Let cool on a wire rack.

For the glaze

• If you want to add the glaze, combine the preserves, water, and gelatin in a small saucepan. Heat to boiling, then continue to boil, stirring, for 2 minutes, until uniformly mixed and slightly thickened. Brush on the brownies while they are still warm.
  1/2 cup apricot preserves, 1/2 cup water, 1/2 teaspoon unflavored gelatin
• Let the brownies cool completely before slicing and serving. You can speed this up by placing them in the refrigerator for 2 hours.