Peel the mangoes, cut the pulp from the stone, cut 400 g of it into small cubes and mix with the preserving sugar in a larger saucepan. Cut the vanilla pod lengthways, scrape out the pulp and stir the pulp into the mangoes. Now halve the oranges, squeeze them out and measure out 550 ml of juice. Mix the orange juice with the mango mixture, finely puree with a hand blender and bring to the boil while stirring. Let the mixture boil for another 4 minutes, skim off any foam and make a gelling test.
Fill the jam to the brim in 4 twist-off glasses, close tightly, turn upside down, turn over again after 10 minutes and let cool down completely.