01 - Line an 8-inch bowl with plastic wrap, leaving enough overhang to cover the top.
02 - Pack the softened vanilla ice cream into the lined bowl, smoothing the surface. Cover and freeze for at least 3 hours until solid.
03 - Place the sponge cake on a parchment-lined baking sheet. Unmold the frozen ice cream dome onto the center of the cake and remove the plastic wrap.
04 - Return the cake and ice cream to the freezer while preparing the meringue.
05 - In a clean bowl, beat egg whites with cream of tartar until soft peaks form. Gradually add sugar, beating until stiff, glossy peaks develop. Incorporate vanilla extract.
06 - Set the oven to 500°F (260°C) or preheat the broiler on high.
07 - Rapidly cover the ice cream and cake completely with the meringue, sealing all edges. Use swirls for decorative effect.
08 - Bake or broil for 2 to 5 minutes, monitoring closely until the meringue turns golden brown.
09 - Serve immediately, slicing with a sharp knife.