Peel an orange and remove the pulp from the skins, collecting the juice. Squeeze the second orange. Bring the orange juice to the boil with 1 tablespoon of jam. Add orange fillets and divide between 4 glasses.
Hollow out the avocado. Puree the pulp with lime juice. Mix in buttermilk, quark and gelatine fix and stir for 1 minute. Stir in the rest of the jam and fructose. Spread the mousse over the 4 glasses and chill for about 2 hours.