I chop up a couple of pounds of onions, a little garlic, sweat them off to they start to brown and aid the caramelisation with a little brown sugar added. As they reach that nice brown toastie stage, I then add a large glug of sherry and let the onions absorb that and scrape the pan to get off all those nice gooey bits. If you have Noilly Prat, I go 50-50 with the sherry.....
Then it is a good beef stock - if you don't have your own then buy one, (low in salt as possible.........
Add that and let it nurdle away - better to make today for tomorrow.
Then little slices of a baguette with something like an emmenthal over it to serve in the top of the bowl, - flash the bowls under the grill before serving to get the cheese nice and runny.