My dessert is chopped up bits of fruit swimming in plain fat-free chilled yogurt (which replaces icecream), which is about 220 Kj per 100g. Any fruit will do as long as its kilojoule count is not high. For example, a chopped up banana, apple and 200g yogurt is about 1200Kj. The bonus over other desserts is that it is very low in fat and relatively high in fibre, while having enough flavour and sweetness.
To even further reduce kilojoules, boil up an apple stew with 50% apple and 50% choko. Chokos are more nutritious than apples, have less than half the kilojoules, and absorb the flavour so well that all mixed up it's hard to tell the difference.
However, if I have dessert I usually reduce my main meal to compensate.