I think you could make just about any onion soup recipe but substitute a really good vegetable broth instead of the beef broth. There are also some "beefless" broths that might have the zing you're looking for. I found the real secret to onion soup is in the cooking of the onions; if you haven't tried this, do, and see if it helps: cook the onions (the pungent yellow ones, not sweet ones) over a very low flame in just a bit of (butter is yummy here but you could use your favorite) oil or if you're foregoing fats, use a small amount of vegetable broth. The trick is to cook them very slowly for 40-45 minutes. Brings out tons of flavor and also brings out the sugars in the onions - the flavor is heavenly. Stir from time to time to keep from sticking. I use a non-stick skillet.

Here's a recipe if you'd like to try what I've always liked:

1/4 c. butter/oil/broth (I use a bit of butter and some broth)
3# thinly sliced yellow onions
1 T. flour (I use more)
apx. 8 c. broth
1/3 c. wine (dry red)
dash white pepper
1 T. thyme
dash nutmeg

Cook onions as described. hen done, sprinkle flour over onions, cook 2 more minutes. Add remaining ingredients; simmer, covered, 30 minutes.

From there, if you like, ladle into bowls and top with traditional french bread slices and Swiss cheese and broil or bake until cheese melts.

I have never been big on onion soups, but Dh and I tried this recipe not long ago and it's wonderful!

2 Tbs. butter
4 large yellow onions, thinly sliced
1 tsp. salt
1/2 tsp. dry mustard
a dash or two of thyme
4 cups water
2 Tbs. soy or Tamari sauce
2-3 Tbs. dry white wine (opt)

Toppings:
thin slices of swiss cheese
croutons

Melt butter in a kettle or dutch oven. Add onions and salt, and cook over medium heat about 10 minutes, stirring occasionally.

Add mustard and thyme, stir and cover. Continue to cook very slowly for about 35 minutes. The onions will be soft and simmering in their own liquid.

Add water, soy sauce or Tamari, optional wine and simmer at least 10 minutes more. Taste to adjust seasonings. Serve topped with croutons and swiss cheese if desired. If you're serving the soup in oven proof bowls you can put them under the broiler briefly to brown the cheese.