Preheat the oven at 350 F. In a bowl, take sliced mangoes or any other fruit, toss in the rose petal jam, sugar, lemon juice, corn starch and mix it well. Transfer it to a baking dish or 4 ramekins or small ball jars .
In another bowl, take the flour, cardamom, sugar, salt, baking powder and cut the chunks of butter into the flour making a crumbly mixture , add the pistachio as well. you can keep this mixture in the fridge if you are going to make this later on.
When ready to assemble just take the fruit in the baking dish, sprinkle the crumble mixture evenly on the fruit by covering every nook and corner.
bake the crumble for about 25-35 minutes until the fruit is bubbling and the crumble looks slightly firm and golden in color. Remove it from the oven and let it come to room temperature and serve it with a dollop of whipped cream, yougurt or cardamom flavored creme anglais e.