One pot lamb and quinoa biryani

Name: One-pot lamb and quinoa biryani
Ingredients: 1 cup yoghurt; 4 cloves garlic, crushed; 1 tbsp grated ginger; 2 tbsp garam masala; 1 tsp turmeric; 1/2 tsp chilli powder; 1kg lamb leg, cut into 5cm pieces; ¼ cup vegetable oil; 1/2 cup cashew nuts; 5 brown onions, finely sliced; 1 cinnamon quill; 1 tsp salt; 2 cups basmati rice; 1 cup mixed quinoa; 2 potatoes, peeled and cut into wedges; 1 1/2 cups milk; a pinch of saffron; 1/2 cup sultanas; 50g butter; coriander leaves and 1 cup coriander raita (see samosa recipe) to serve