Shepherds pie with spiced parsnip mash

Name: Shepherd's pie with spiced parsnip mash
Ingredients: 900g/2lbs large parsnips, peeled and cut into large chunks; 2 onions, sliced; 50g/2oz butter; Large pinch ground cumin; 1 tbsp freshly ground coriander seeds; 1 tbsp garam masala; About 50g/2oz butter; Salt and freshly ground black pepper; 2 leeks or onions, chopped; 1 carrot, diced; 3 tbsp dripping or butter; 4 italian brown mushrooms, sliced; 450g/1lb cooked roast lamb, minced, or raw lamb mince; 1 tbsp flour; 1 tbsp tomato purée; 250ml/9 oz hot lamb or chicken stock; 1 bay leaf; 1 sprig thyme; 1 tbsp worcestershire sauce