I have just re-discovered this recipe, and wanted to share it with you. It's somehow for me a holiday recipe because of all the chopping of onions, and it always seems like a 'special' soup rather than an everyday one, but I have to say it was brilliant for warming us up at the weekend - so I recommend you give it a try in this very cold spell!
My usual mistake is not having the heat high enough to caramelise the onions, they need to go a nice brown but with plenty of butter and oil shouldn't stick too much - just keep moving them around. (Not a good diet recipe, especially with the toasted cheese!) I never bothered with making croutons as it says, we just toasted french bread one side then turned it over and piled on grated gruyere before putting it back under the grill, then floated it in the soup bowls afterwards (you can see ours didn't really quite fit). We didn't add brandy either because the boys were having it, but I bet it's good with it in!