Sift the flour into a bowl, crack the egg in the centre and add salt and pepper to taste. Gradually whisk in the milk until smooth. It can stand a while.
Coat the sliced onion in oil and sugar and spread over a baking tray. Put the sausages in a Pyrex glass bowl or a heavy bottomed roasting pan and put both in the oven.
When the sausages are cooked (10-15 minutes) add a spoon of oil then pour in the batter. Return to the oven and bake 30 minutes.
Heat the stock in a small saucepan. Add the Worchestershire sauce and mustard powder. When the onions are blackening, sprinkle them with the flour and add them to the stock, stirring with a fork until smooth.
Serve the sausages and batter with the onion gravy poured on top.
I'm a British ex-pat living in Australia who gets the occasional bout of homesickness. This dish is an excellent cure! Equally good without the gravy. My Aussie hubbie enjoys it too, so it's gone into our dinner rotation. Best eaten with a glass of Boddington's or Newcastle Brown Ale. - 11 Oct 2014