Cut the walnuts into small pieces. Mix the sugar with the milk until it dissolves. Scrape out the vanilla pod and mix the pulp with the milk. Now mix the milk with the quark.
Peel the mango and cut into large pieces. Puree the mango pieces together with the lemon juice with the hand blender. Distribute the mango mixture and the quark decoratively in dessert bowls and chill for about 1 hour.