1. Combine the biscuit crumbs, fine white chocolate and melted butter and press in to the base of an 8-inch spring form cake tin and all the way up the sides. Freeze for 30 minutes.
2. Place the softened ice cream, cream cheese, sugar, lime juice, zest and optional green food colouring in to a bowl. Use a whisk to beat until fully combined. Pour on top of the frozen crumbs. Freeze for 2-3 hours.
3. To make the meringue topping, combine the water and sugar in a small pan. Heat until a candy thermometer reaches 115°C. Don’t stir the syrup while it cooks.
4. Wipe the inside of the bowl with the lemon wedge. Add the egg whites and whip for 2 minutes until you have soft peaks. Add the lime zest and cream of tartar.
5. Next, with the mixer on at full speed, slowly pour in the sugar syrup and whip until you have a thick, glossy meringue.
6. When ready to serve, pile the meringue on top of the ice cream.
8. Place the pie on a heatproof worktop and blowtorch the top until lightly golden. Slice and serve.