This recipe originally comes from The British Food Bible. I have used the recipe on several occasions with good results. I think, I like it best, made with Port. I have tweaked the recipe on occasion using a spoon of marmite or vegemite with some boiled water when I was out of liquid stock. The recipe below has my adaptations in italics.
Onion Gravy
adapted from The British Food Bible
3 onions, sliced thinly - I use two softball size red onions
70g butter - I use 50g I find the full amount is too much
125ml Marsala, port - I like port best it is not as sweet as the Marsala.
125ml vegetable stock - My family likes it best with Marmite or Vegamite mixed in boiled water to make stock.
salt and pepper
Brown the onions in the butter on medium heat until soft and caramelized. Pour in the port or Marsala and the stock. Stirring occassionally let the liquid reduce to a lovely thick sauce. Season with salt and pepper to your taste.