Melt the butter in a saucepan or frying pan then add the onions in.
Cook for 1-2 minutes then sprinkle with the sugar.
Stir regularly while cooking on a medium heat for 10-15 minutes. You’ll know when the time is up as the onions will be soft and they will have become caramelised thanks to the butter and sugar.
Sprinkle the flour over the onions. Give it a stir to ensure that all the onions are coated. Cook for a further 1-2 minutes.
Pour in your stock if using fresh. If you’re using a stock cube then save yourself some effort by crumbling the stock cube in and then measuring in the required water.
Bring the onion gravy to the boil. Reduce the heat to a simmer and allow the onion gravy to thicken up. Add a splash of Worcestershire sauce. If it needs a little more seasoning then add a grind of fresh black pepper.