Martha Stewart Brownie Sundae Ice Cream Cake

Directions

• Prep the pan: Preheat the oven to 375°F, then coat a 9-by-13-inch baking pan with cooking spray. Line it with parchment, leaving overhang on the long sides, and spray the parchment too.
• Mix the dry ingredients: Whisk 2/3 cup all-purpose flour, 1/4 cup Dutch-process cocoa powder, 3/4 teaspoon coarse salt and 1/2 teaspoon baking powder in a bowl. Set it aside while you make the batter.
• Cream the butter: Beat 1 stick room temperature butter with 1 cup sugar on medium speed until pale and fluffy, about 3 minutes. Then add 2 large eggs one at a time, beating until smooth, and beat in 1 teaspoon vanilla.
• Finish the batter: With the mixer on low, add the flour mixture in three batches, alternating with 1/3 cup whole milk in two additions. Beat in 4 ounces melted bittersweet chocolate once everything is combined.
• Bake the brownie: Spread the batter into the prepared pan with an offset spatula, then bake about 15 minutes. It's ready when the top is set but the center is still wobbly, so cool it completely in the pan on a wire rack.
• Cut the brownie: Line an 8 1/2-by-4 1/2-inch loaf pan with plastic wrap, then use the parchment to lift the brownie out. Cut it crosswise into 3 pieces: one that fits the bottom exactly, one slightly wider and one widest of all to match the pan as it widens.
• Layer the cake: Place the smallest brownie piece top-side up in the loaf pan, then spread on 1/2 cup crunchy peanut butter and 1 1/4 cups softened vanilla ice cream. Add the second piece top-side down, spread with 1/3 cup crushed raspberries and 1 1/2 cups softened strawberry ice cream, and top with the last piece top-side down.
• Freeze until firm: Cover the pan with plastic wrap and freeze at least 6 hours and up to 1 day. This gives the ice cream time to set so the stripes slice cleanly.
• Unmold and decorate: Run a butter knife around the edges, then lift the cake out by the plastic and set it on a platter. Top with lightly sweetened whipped cream and sugared peanuts.
• Slice and serve: Slice with a sharp knife, wiping the blade clean between each cut. Serve every slice with a few more sugared peanuts and a maraschino cherry.