By asaylor, member
Posted: November 15th, 2011
Position a rack in the center of the oven and heat the oven to 325 degrees F. Line the bottom and sides of a 9x13-inch straight-sided metal baking pan with heavy-duty aluminum foil, leaving about a 2-inch overhang on the short sides. Lightly butter the foil.
Put the butter in a large (4-quart) saucepan over medium-low heat and stir occasionally until melted, about 2 minutes. Off the heat, whisk in the cocoa powder until smooth, 1 minute. Add the sugar and salt, and whisk until well blended. Use your fingertip to check the temperature of the batter -- it should be warm, not hot. If it's hot, set the pan aside for a minute or two before continuing.
Whisk in the vanilla extract and then the eggs, two and then three at a time, until just blended. Sprinkle the flour over the batter and stir with a rubber spatula until just blended. Stir in the peanut butter chips and white chocolate chips.
Scrape the batter into the prepared pan and spread evenly. Drop the peanut butter by tablespoons evenly over the top and, using a knife or small spatula, swirl into the batter. Bake until a toothpick inserted in the center comes out with small bits of brownie sticking to it, 35 to 45 minutes. Do not overbake. Cool the brownies completely in the pan on a rack, about 3 hours.
Put the chopped bittersweet chocolate and butter in a small, heatproof bowl set over a small pot of barely simmering water and stir frequently until melted, about 3 minutes (alternatively, the chocolate and butter can be melted in a microwave).
Using the foil overhang, lift the brownies from the pan. Invert onto a cutting board, carefully peel away the foil, and flip again. Pour the glaze over the brownie and spread to within 1/2 inch of the edges using a small offset spatula. Sprinkle the walnuts over the glaze. Set the brownie aside until the glaze is firm. Cut the brownie into 24 squares and serve immediately, or wrap in in plastic or waxed paper and refrigerate for up to 5 days. Let the brownies come to room temperature before serving.