Belgian Beer Onion Gravy

This recipe started as another experimental creation that worked out well. We recently bought some fantastic Pembury Porkers sausages from this farm shop on the way back from a camping trip. Grilled up with some mashed potato and onion gravy, this was an excellent way to finish the bank holiday weekend.

Ingredients
1 tsp oil
1 large onion, sliced
couple of sprigs of rosemary
couple of bay leaves
330ml bottle of Gulden Draak or other dark, Belgian beer.
beef stock cube (optional)
1 tsp agave syrup, sugar or honey
Worcestershire Sauce to taste
Good quality vinegar to taste
salt and pepper to taste

1. Over a medium heat fry the onions with the bay leaves and rosemary until they have taken on a golden colour with some decent crispy bits. This will probably take around 10-20 minutes. The longer you take over this the sweeter the final flavour will be. Colour on the onions intensifies the flavour of the gravy. 
2. Open and carefully pour in the Gulden Draak beer. It will probably bubble up a little but this will quickly subside. Add the beef stock cube if you're using it then cook the beer down until the smell of alcohol is gone and the liquid has reduced a little. This will be around 5 minutes depending on the heat you're using.
3. Taste your gravy carefully, it will be very hot, and adjust the flavour according to your taste using the sugar, worcestershire sauce, vinegar and salt and pepper. I put in 1tsp of agave, roughly  1 tbsp of Worcestershire sauce, 2 tsp white wine vinegar and a good sprinkle of freshly ground black pepper. I did not add any salt. 
4. Cook for another minute or two to help the flavours mix together, then serve.