1 large onion, finely chopped
700g/1lb 9oz potatoes, peeled and cut into halves or quarters
2 fresh thyme sprigs
1 anchovy, finely chopped (optional)
400g tin chopped tomatoes
1 tbsp plain flour
2 tsp Worcestershire sauce
2 bay leaves
salt and freshly ground black pepper
2 tbsp olive oil
25g/1oz vegetable oil or beef dripping
85g/3oz butter
1 free-range egg yolk
55ml/2fl oz milk
500g/1lb 2oz lamb mince
450ml/16fl oz chicken, beef or lamb stock