I haven't, but it sounds pretty darn good.
Our favorite onion soup is Walkabout Soup clone recipe, but it's got flour in it to thicken. Since I'm not GF, I don't know if there's anything else in there that you couldn't eat -
Outback Steakhouse Walkabout Soup
4 servings
2 cups yellow sweet onions, Thinly Sliced
2 tablespoons butter
1 (15 ounces) can chicken broth
1/4 teaspoon salt
1/4 teaspoon fresh pepper, Ground
2 chicken bouillon cubes
1/4 cup Velveeta cheese, Cubes, Diced, (compressed in measuring cup)
1 1/2-1 3/4 cups white sauce (Below)
cheddar cheese, Shredded (for garnish)
White Sauce:
3 tablespoons butter
3 tablespoons flour
1/4 teaspoon salt
1 1/2 cups whole milk
In 2 quart sauce pan place 3 tablespoons butter and sliced onions.
Cook at low to medium heat stirring frequently until soft and clear but not brown.
Add chicken broth from can, chicken bouillon cubes, salt, pepper, and stir until completely heated through.
Add white sauce and Velveeta cheese. White sauce will be thick because it has been remove from the heat. Simmer on medium low heat until the cheese is melted and all ingredients are blended, stirring constantly.
Turn temperature to warm and let cook for additional 30 min. to 45 min.
Thick White Sauce:
In a 1 quart sauce pan melt butter and add flour, cook on medium heat until the flour turns thick and comes away from the side of the sauce pan.
Pour milk in flour a little at a time and stir constantly, add salt. Mixture should thicken and become like thick pudding.
Remember to stir constantly taking care not to let mixture lump, set aside off from heat until ready to use for the soup.