Caramelize the sugar in a frying pan until light brown. Add the walnuts, stir gently. Place the caramelized walnuts on a baking tray lined with parchment paper and cool around them (not in the icebox), then chop coarsely.
Whip 1/5 of the whipped cream with the maple syrup and the egg yolks over a hot water bath until creamy, then chill in a cold water bath.
Soak the gelatine in cold tap water. Warm the cognac, squeeze the gelatine properly, melt it in the cognac, then quickly fold it into the egg cream together with the chopped nuts. Whip the remaining whipped cream until not too stiff and fold it in.
Cover the baking dish with cling film, pour in the parfait mixture and freeze for at least 12 hours.
For the compote, defrost the plums in a sieve and add the juice. Cut the plum halves in half. Grate the orange skin thinly on a household grater. Cut the orange in half and squeeze out the juice.
Caramelize sugar in a frying pan, add plums with juice, orange skin, juice and marinade. Cut the preserved plums in half, pit them and add to the compote with the cinnamon stick. Cook 1000 cmin weakly on the stove until the caramel has dissolved. Finally, mix the cornstarch with the juice of one lemon and thicken the compote with it. Remove from heat and refrigerate until ready to serve.
To serve, remove the parfait from the foil.