Make the ice cream cake: Brush a 3-quart metal bowl with vegetable oil; line with plastic wrap. Fill the bowl with scoops of the sorbet, vanilla ice cream and half of the chocolate ice cream, alternating small and large scoops to create a mosaic of colors and shapes. Place a piece of plastic wrap on top of the ice cream; press down to close the gaps between scoops and even out the surface. Remove the plastic wrap, sprinkle the ice cream with the wafer crumbs and re-cover with the plastic wrap, pressing gently. Freeze until set, about 30 minutes.
Remove the wrap and spread the remaining chocolate ice cream in an even layer on top of the crumbs. Cut the pound cake into 1/2-inch-thick slices; completely cover the ice cream with the slices, trimming as needed (you'll use about two-thirds of the cake). Cover with fresh plastic wrap and freeze until firm, at least 2 hours or up to 2 days.
Make the meringue: Whip the egg whites and cream of tartar in a large bowl with a mixer on medium-high speed until foamy, about 2 minutes. Gradually beat in the sugar on high speed until the whites are glossy and hold stiff peaks.
Remove the top layer of plastic wrap, then invert the cake onto a parchment-lined baking sheet. (If necessary, let the cake stand overturned until it slips out.) Remove the rest of the plastic wrap and cover the ice cream completely with the meringue, making the dome-shaped top slightly thicker than the sides. Form swirly peaks in the meringue using the back of a spoon. Freeze for at least 3 more hours.
Preheat the oven to 500 degrees. Bake the cake until the meringue peaks are golden, about 4 minutes, or brown the meringue with a blowtorch. Let the cake soften at room temperature for 5 to 10 minutes before slicing. Freeze any leftovers.