For rice, run the rice under cold water until water runs clear through it. Transfer to a bowl and cover with water then stand at room temperature for 1 hour. Once rice is done resting, drain it.
In a skillet, heat the butter on medium until melted. Add the onions and fry for 5 minutes or until softened. Add the spices and cook stirring until fragrant (30 seconds). Add the rice and stir to coat. Add 2 cups of cold water, bring to the boil then reduce to a simmer for 6 minutes or until all water is absorbed. Remove from heat and set aside.
For jackfruit curry, remove the jackfruit from the can and shred with two forks then run it under cold water for 5 minutes. Meanwhile, in a skillet, heat the butter on medium and fry the onions for 10 minutes or until just starting to brown. Add the garlic and spices then fry stirring for a further 1 minute. Add the tomatoes and deglaze the pan.
Add the shredded jackfruit and bring to a simmer. simmer uncover for 20 minutes or until thickened.
Preheat oven to 180°in a casserole dish construct the biryani by alternating layers of curry and rice. Cover with foil then bake for 40 minutes. Serve topped with vegan yogurt.