A delicious dessert that's fun to make. The kids will go wild over the idea of a brownie-crusted ice cream pizza.
Line a large cookie sheet with aluminum foil. Lightly butter the foil and set it aside. Finely chop the nuts and set them aside.
Melt together the butter and chocolate in a double boiler (or in the microwave at half power, stirring every 30 seconds), stirring until smooth. Set aside to cool.
Beat the sugar and eggs on high speed in a large bowl for about 5 minutes. Blend in the melted chocolate and vanilla extract until smooth. Stir in the nuts. Mix together the flour, baking powder, and salt. Add them to the chocolate mixture and stir until evenly blended. Let the dough sit for 2 to 3 minutes.
Scrape the dough into the center of the buttered foil. Spread the dough into a more or less level circle 12 inches in diameter. Refrigerate for 10 minutes while you heat the oven to 350º.
Bake the crust on the center oven rack for 13 minutes. Transfer it to a cooling rack and cool it until it is just warm to the touch. Invert the crust onto a second cookie sheet, then gently peel off the foil. Invert it again onto the sheet or a serving tray and refrigerate for 30 minutes.
Smooth a layer of slightly softened ice cream 1/2 to 1 inch thick evenly over the crust. Decorate with canned whipped cream and candies (if you're presenting the pizza whole, consider using lines of whipped cream to draw slices). Transfer the pizza to the freezer until you're ready to slice and serve.