Peel the oranges, remove the white outer skin and cut into large pieces (catch the juice that comes out and add to the cooking mixture). Remove cores if necessary. Place in a large saucepan with the bananas cut into pieces, lemon juice, tonka bean zest, vanilla pulp, grated ginger and the preserving sugar and puree everything. Bring the mixture to the boil while stirring. Let cook for at least three minutes. Then immediately fill into prepared glasses.