Here is my fat-free dairy-free version.
Cut a baguette into 1" pieces on the diagonal.
Toast them on both sides in the broiler. Set aside.
Slice 3 cups yellow onions thinly and saute on medium-low in 1/4 cup of water for 15 minutes. Stir to make sure they are browning, not burning.
After 15 minutes, add 1/4 teaspoon sugar and 1/2 teaspoon salt. Let cook for an additional 20 minutes with the lid on. Check a couple of times for burning.
Add 4 cups of vegetable broth, 1/4-1/2 cup white wine of choice, and a couple of dashes of maagi soup starter for color. You could use 1/8 teaspoon soy sauce for color instead of the soup starter. You just want to get a nice deep caramel color in the broth. Cook on medium-low for 40 minutes.
In your soup bowl, place 2 toasted baguette pieces. Spoon soup over it. Eat.
If you just have to have a cheese replacement, try using one of the swiss flavored almond-based cheeses, as they seem to melt. If you do this, put the baguette pieces in an oven-safe bowl, spoon the soup on, put the fake-cheese slice on top, and broil in the broiler until it is melted and slightly browned on top. Then eat.