Congo Brownies - baking powder

Method

• Before baking:
• Center a rack in the oven and preheat the oven to 350 degrees F. Lightly butter a 13 by 9 by 2-inch pan (quarter sheet pan), then flour it, tapping out the excess flour.
• To make the Congo Layer:
• Sift together the flour, baking powder, and salt onto a sheet of waxed paper; set aside.
• In a large bowl, stir together the butter, brown sugar, egg, egg white, and vanilla just until blended.
• Stir in the flour mixture just until the batter is smooth.
• Scoop the thick, sticky batter onto 8 or 9 different areas on the bottom of the prepared pan.
• With an offset spatula, spread the batter to cover the pan as evenly as possible.
• Sprinkle the walnuts evenly on top and gently press them into the batter.
• Partially bake the layer until it is no longer shiny on top and is beginning to come away from the sides of the pan, about 20 minutes.
• Transfer the pan to a wire rack to cool while you prepare the Brownie Layer.
• To make the Brownie Layer:
• Sift together the flour, cocoa powder, baking powder, and salt onto a sheet of waxed paper; set aside.
• In a small, heavy saucepan, melt the butter and chocolate over very low heat, stirring with a silicone spatula until smooth.
• Or, combine in a medium microwave-safe bowl and melt in a microwave oven at 50 percent power (medium) for 30-second bursts, stirring after each burst, until melted, 1 to 1 1/2 minutes.
• Transfer to a medium bowl and let cool for 5 minutes.
• Stir the sugar into the chocolate mixture until incorporated.
• Add the eggs, egg yolk, and vanilla and stir until well blended.
• Stir in the flour mixture just until the batter is smooth.
• Scoop the thick, sticky batter onto 8 or 9 different areas of the still-warm Congo Layer.
• With the offset spatula, spread the batter as evenly as possible.
• Bake the brownie until the top is no longer shiny; appears set; feels firm, rather than soft; and a round wooden toothpick inserted in the center comes out with moist chocolate crumbs attached, about 25 minutes.
• Transfer the pan to a wire rack and let cool completely.
• The top layer will set up as it cools.
• To make the Chocolate Glaze:
• Place the chocolate in a medium bowl.
• In a small saucepan, bring the cream just to a boil over medium-low heat.
• Pour the cream over the chocolate and let it stand for 30 seconds.
• Whisk together until smooth and creamy.
• Set the mixture aside at room temperature just until it cools a bit and begins to thicken slightly.
• Fashion a small cone out of parchment paper and half fill it with the liquid glaze.
• Snip a small opening at the end of the paper cone to allow a thin flow of glaze.
• Exerting light pressure on the cone, and never easing the pressure or halting the motion, pipe thin lines of chocolate in a zigzag pattern over the cooled surface of the brownie.
• Set aside at room temperature until the glaze is set, 1 to 1 1/2 hours.
• To serve, cut the brownie lengthwise into seven 1 3/4-inchwide strips, and then cut crosswise into seven 1 1/4-inch-wide strips, to yield forty-nine 1 3/4 by 1 1/4-inch bars.
• Or, cut lengthwise into 6 strips and crosswise into 4 strips to yield twenty-four 2-inch squares.