Chill a baking tray in the freezer for 10 minutes.

Loosen the ice cream in its tub with a long knife and invert it onto the chilled tray. Return to freezer for 30 minutes.

Cut a disc from the sponge cake using the tub's lid as a guide and place it on a separate baking tray.

Lower the frozen ice cream onto the sponge disc, widest-end down, and chill in the freezer for 30 minutes.

In a saucepan, stir together water and sugar over low heat until sugar melts.

Increase heat to medium-high and bring syrup to 115°C (soft ball stage).

While the syrup heats, whisk egg whites and cream of tartar until soft peaks form.

Once syrup reaches 120°C (hard ball stage), drizzle it into the egg whites while beating on low speed. Continue whisking for 10 minutes until thick and glossy.

Spread half of the meringue over the ice cream and cake and freeze for 10 minutes.

Cover the cake with the remaining meringue.

Use a blowtorch to caramelize the meringue just before serving.

Serve sliced, drizzled with caramel sauce.