01 - Line an 8-inch diameter bowl with plastic wrap, leaving excess on edges. Press the softened vanilla ice cream evenly into the bowl, smoothing the surface. Freeze until very firm, at least 2 hours.
02 - Trim the sponge cake to match the diameter of the ice cream dome. Unmold the ice cream from the bowl using the plastic wrap and invert onto the cake base placed on a parchment-lined baking sheet. Freeze the assembled cake and ice cream dome until firm, approximately 30 minutes.
03 - Preheat the oven to 450°F.
04 - In a clean, dry mixing bowl, beat egg whites with cream of tartar until soft peaks form. Gradually add granulated sugar while continuing to beat until stiff, glossy peaks develop. Incorporate vanilla extract and mix briefly.
05 - Remove the ice cream dome on cake base from freezer. Quickly cover it entirely with meringue, sealing the base and creating decorative swirls using a spatula or spoon.
06 - Bake in the preheated oven for 5 to 8 minutes, until the meringue turns golden brown. Monitor closely to prevent burning.
07 - Serve immediately, slicing carefully with a sharp knife.