Mix the pork in a bowl with the ginger, garlic, garam masala, chili powder, tumeric, chillies, mint and coriander. Cover and refrigerate overnight.
The next day, put the sliced onion in a colander, sprinkle with salt to draw liquid out of the onions. Discard liquid, rinse onions and pat dry.
Heat oil and butter in a dutch oven, then fry onions until golden brown (about 10 minutes). Remove onions and drain. Pour off and reserve all but about 2 tbsp of the butter and oil.
Fry the pork in the dutch oven until well browned. Add cooked onions and yogurt and cook on low for 40 minutes.
In a large saucepan, boil enough water to cover rice. Add rice, return to the boil, and cook 5 minutes.
Drain rice, spread on top of onions and pork in dutch oven. Drizzle with lemon juice, saffron/milk mixture, and the leftover butter and oil.
Preheat the oven to 425 Fahrenheit.
Make a dough by adding a little water to the flour and 1 tsp salt. Roll dough into a long, thin sausage shape, and press along the top rim of the dutch oven. When the lid is placed on this dough, it will form a seal between the lid and base of the dutch oven.
Cook sealed dutch oven on high heat for 5 minutes before transferring to oven. Bake in oven for 40 minutes.