French Onion and Mushroom Rice Casserole

This casserole is so yummy!  I think I would have died if Mom made it when I was younger - all those onions!  But they're cooked until they're soft in this recipe and the flavor is awesome.
Plus, it doesn't use French Onion Soup mix.  I think the mix tastes okay, but it always leaves a funky aftertaste that lasts for a full day.  Yuck.
I very slightly altered this from http://iowagirleats.com/2015/09/08/creamy-french-onion-mushroom-rice-casserole/

French Onion and Mushroom Rice Casserole

Ingredients

• 5 ½ cups rice, cooked (mix of brown and white)
• 3 Tablespoons butter
• 1 jumbo sweet onion or 2 small sweet onions, chopped
• 1/2 cup beef broth
• 1 Tablespoon gluten-free Worcestershire sauce
• 3/4 teaspoon dried thyme
• 1/2 teaspoon sugar
• 1 bay leaf
• salt and pepper
• 8oz mushrooms, thinly sliced
• 3 cloves garlic, minced
• 5 teaspoons flour
• 2 cups milk, divided
• 6oz shredded fontina (or Monterey jack) cheese, divided
• 1/4 cup + 2 Tablespoons freshly grated parmesan cheese, divided
• 1/3 cup regular or light sour cream

Directions

1. Spray a 9x9" baking dish (or equivalent-sized baking dish) with nonstick spray then set aside. Place a large skillet over high heat then add butter, onions, beef broth, worcestershire sauce, dried thyme, sugar, bay leaf, salt, and pepper. Bring liquid to a boil then turn heat down to just a touch above medium and simmer until onions begin to soften and broth is nearly absorbed, 10 minutes, stirring occasionally.
2. Add mushrooms to skillet with onions then turn heat up to medium-high and saute until mushrooms are tender, 5-7 minutes. Add garlic, season with salt and pepper, then saute for 1 more minute. Remove bay leaf then scoop mixture onto a plate and set aside.
3. Whisk together flour and 1/2 cup milk in a small dish then pour into skillet. Add remaining 1-1/2 cups milk, season with lots of salt and pepper, then let the mixture come to a bubble, stirring constantly. Turn heat down to medium then simmer until liquid is thickened and bubbly, 8-10 minutes, stirring constantly. Remove skillet from heat then stir in 4oz fontina cheese, 1/4 cup parmesan cheese, and sour cream. Taste then add salt and pepper if necessary.
4. Add the cooked rice and mushroom/onion mixture to the cheese sauce then stir to combine and scoop into the prepared baking dish. Top with remaining shredded fontina and parmesan cheese, then broil until golden brown.