Make it several days ahead! No, it will not loose anything but will possibly gain something. Caramelize the onions until a dark brown knotty lump, don't skimp on the liquor, and add the topping/croutons at the last minute.

Thank you so much Bumblebeez! I usually do this for stews, Julia's Boef Bourg., etc., but wasn't sure about her French Onion Soup...and her recipe doesn't say anything about this. I've made this recipe many, many times and you are so right...the secret is the caramelization of the onions (and the liquor merely adds GREAT flavor). You've made my Entertaining Day so much easier with this advice!

I make Julia's recipe to the letter, including the amount of Cognac, and a friend of mine said it tasted like it was 40 proof. I would definitely NOT increase the alcohol - Julia's recipe uses plenty - at least the one I have does. I may have added the Cognac too late in the process, however.

I agree that it is better to make it ahead of time - it gives the alcohol a bit more time to evaporate.

Lars

I don't increase the alcohol but I do use what the recipe states, although I use French Brandy and not cognoc.
Ok, wait a moment, I think I do add about a cup of red wine in addition to the vermouth.. Ina's recipe is boozier.

Onion soup is the easieet thing in the world! I mass-caramelize the onions in a slow cooker and then divide and freeze them for soup in the future. Slow cooker instructions: pile sliced onions in cooker, turn it on to LOW, leave it alone for 10-14 hours.

I make it a day or two in advance all the time.

I know I don't need to tell you this , but for the sake of any lurkers , we are talking about the broth and onions. The bread and cheese should be added just before serving.

Just to clarify. French brandy is cognac. It's the name of the place it's made.

I'm interested in making a big batch of onions and splitting it into portions for the freezer. Two questions for those that have tried the crock pot:

1) Do you add any fat to the onions?
2) I'm not imagining too much in the way of "browned bits" to deglaze, and so I'm wondering, how much does that affect the flavor?

French Onion soup can be great or just good but as it's my favorite soup and also freezes magnificently, I put effort into deeply, slowly caramelizing the onions. It can take 1 and 1/2 hours to caramelize the onions to a dark walnut without burning them. I can't imagine this flavor could be replicated in a crock pot.
I'd have to check the recipe to be exact, but offhand for 5 pounds of yellow onions, I use 10 tablespoons of butter, 1/4 cup oil, 1/4 cup sugar and salt. This being a double recipe.

I regularly caramelize onions in my crockpot. I slice enough onions to fill it, which is about 5 lbs or so. I get a bag from Costco and do the whole lot, sometimes in 2 batches. I add a stick of butter and turn it on. At the start the onions give off liquid so you get a soupy mix, but as the liquid is cooked off, you'll see the onions caramelize in their own sugars. I don't add anything, no sugar, no salt. I don't find it necessary but your taste may not be the same as mine.

Once it's deeply caramelized (for me it takes most of a day), you can do whatever you like. We freeze in portions to be put on pizza, or eaten with tortillas, or added to soups, stews or sauces.

Cheryl

I really like the idea of having caramelized onions on hand, and like the idea of using a slow cooker!

Cheryl, is that cooked on High or Low?

jasdip - I start on high and keep it there until most of the liquid is cooked off. Then I switch to low until the onions are just about done. If I'm not going to be around to keep an eye on it, I put it on low and let it go. Your slow cooker might not be as low powered as ours, so you should see how long it takes. It's really easy.

Cheryl

My slow-cooker is an orange, round vintage one, so it will be a true slow-cooker. LOL Thanks Cheryl!

Well I filled up my crockpot with onions, ran them on high for a couple hours then turned down to low. Total cook time around 11 or 12 hours. They turned brown but were still swimming in soup and not what I'd consider caramelized. I'm thinking I'll strain and finish up stovetop. I'll reserve the liquid and play it by ear if I use it. Perhaps boil it down a bit and see what happens.

This is a 21st century crock pot so I don't think the problem was running too low.

Put that delicious juice in the soup. If they aren't dark enough for you, let them go a while longer. I do at least 12 hours of crock potting, but they are juicy.

As I posted above, I keep the crockpot on high until all the liquid has evaporated, then turn down. You can turn the crockpot back onto high to reduce the liquid. The onions will caramelize, but it does take a long time. My onions end up without excess juice. I think timing depends on how watery the onions are, and how your crockpot runs.

Cheryl