Spiced parsnip soup

Name: Spiced parsnip soup
Prep time: 30 min
Cook time: 40 min
Total time: 1 h 10 min
Cuisine: British
Ingredients: small knob of butter; 1 onion , sliced; 2 garlic cloves , sliced; small piece fresh root ginger , peeled and sliced; 6 large parsnips , peeled and chopped; 1 tsp cumin seed; 1 tsp coriander seed; 2 cardamom pods; 1 tbsp garam masala; 1.2l vegetable stock; 150ml pot double cream; 1 tsp olive oil; 1 tsp toasted cumin seeds; 1 red chilli , deseeded and sliced; coriander leaves