Spray a decent size frying pan with some low calorie cooking spray and place on a high heat.
Peel the onions. Chop one of them roughly and cut the other one into slices. Peel and chop the carrot.
Season the liver with a little sea salt and freshly ground black pepper. Carefully put the liver in the hot pan and cook for 2-3 minutes. Turn each piece and cook for another 2 or 3 minutes.
Remove the liver from the pan and set aside. Spray the pan with some more low calorie cooking spray. Cook the onion slices until they start to soften and colour. Remove them from the pan and set aside with the liver.
Add the carrots, chopped onion and stock to the pan. Bring to the boil and simmer for 10 minutes. When the onions and carrot are cooked blitz them with a stick blender until smooth. The gravy may be a little orange due to the carrot, so add a couple of drops of gravy browning if you want
Put the liver and cooked onions back into the gravy and cook for another few minutes. Check the liver is cooked to your liking and serve.