1 onion, halved lengthways and sliced
1–2 tsp tomato ketchup
4 tbsp plain flour
1 beef stock cube
salt and freshly ground black pepper
2 tbsp sunflower oil
25g/1oz butter
125g/4½oz rindless streaky bacon rashers, each cut into 4–5 pieces
450g/1lb lambs’ liver, sliced and fully thawed if frozen
500ml/18fl oz just-boiled water