Cut peaches in half and remove stones. Peel and cut pineapple into wedges. Sprinkle fruit with 2 tbsp of sugar and barbecue until golden.
Melt the rest of the sugar in a pan until caramelised, add a knob of butter and tablespoon of water and swirl until heated and melted. Pour over ice cream. Serve with ice cream and the sauce poured over the top.