Heat a soup pot over medium heat and add the butter and oil.
1 tablespoon butter, 1 tablespoon oil
Slice one of the onions as thinly as possible.
4 large onions
Add them to the pot and sprinkle a little salt.
Repeat with each onion, layering them with a pinch of salt in the pot.
Once finished, stir them all together add the bay leaves and let everything slowly cook over medium to medium-low heat for at least 1 hour, stirring about every 20 minutes or so.
2-3 bay leaves
After an hour the onions will have reduced and darkened in color.
Roughly chopped the musrooms and add to the onions with the 1 cup of wine.
1 cup red wine
Let the mushrooms and wine cook down for about 10 minute before adding the beef broth.
1 lb mushrooms, 8 cups beef stock/broth
After adding the beef broth, bring everything to a light boil then lowered to a simmer until ready to serve.
Notes
You can use all sweet onions or vary them. I like to do a mix of sweet, red and spanish.
Use wine you would drink!
I like to use my own beef stock but I've made it successfully with beef broth. If you don't have enough beed broth a mix of beef and chicken would work too but the beef stock adds a deeper flavor.
Use veggie stock to make it vegetarian.
When I do top with cheese I like provolone but you can use any cheese your like. The best is to toast a baguette slice, plot it in and then melt the cheese over top. You can see how I do this is an old IG story I posted last year.
Which reminds me, you could totally skip the mushrooms if you want to make a more traditional French Onion soup. I did last year.