Preheat oven to 500°F (260°C) and line a small baking sheet with parchment.
Trim cake slices to match two small ramekins or metal bowls and brush tops with melted butter.
Scoop ice cream into two tight domes on the cake, then freeze 20–30 minutes until firm.
Whisk egg whites and salt until soft peaks form, then add sugar 1 tablespoon at a time and whip to stiff glossy peaks; fold in vanilla.
Remove cakes from freezer, pile meringue over each ice cream dome, sealing edges to the cake.
Bake 3–5 minutes until meringue is browned, watching closely.
Serve immediately.