Don't use food as a reward. Don't use dessert as a reward for a clean plate. If serving dessert at a meal, serve it at the same time as the other foods and don't be concerned if your child eats dessert first. It can be a fun time, a time of togetherness. Relax and enjoy it.
Kids are naturally suspicious of food mixtures, preferring plain foods kept separate.
But like anything new and different, with time, patience and guidance, they might just try it.