Heat a pan with the oil and butter on the stove. Put onions in as you cut them to get them cooking. As soon as you get all of the onions in the pan give them a good stir to coat with the oil. Put the cover on and place pan in oven.
Stir the onions once an hour. During the last hour I check them a few times and give them a stir. When the onions are golden brown they are done.
Ready now to add the broth and finish.
Remove to top of stove. Add chicken broth and bring to a boil.
To serve: Slice a French baguette into 1 inch pieces. Broil until light brown. Ladle the soup into ovenproof bowls. Top with the baguette slices and top with Gruyere cheese. Put back under the broiler until cheese is bubbly and just starting to turn color.
Recipe by Recipes Food and Cooking at https://recipesfoodandcooking.com/2011/10/31/baked-french-onion-soup/