Creamed Brussels Sprouts, Mushrooms, and Onions

I've made this dish a couple of times and thought I originally found the recipe here on 'Zaar, but after enlisting help to look for it, realized it came from the November 2003 issue of Bon Appetit. This does require a bit of work, but the results are rich and delicious. It's become a Christmas tradition in our home.

• Ready In: 1 hr 25 mins
• Serves: 8

Ingredients

• 5  tablespoons unsalted butter
• 1  lb  oyster mushroom, cut into 1-inch-wide pieces
• 15  ounces  frozen small whole onions (do not thaw)
• 1  lb  small Brussels sprout, trimmed and halved
• 2 1⁄2 cups low sodium chicken broth
• 2  garlic cloves, minced
• 1 1⁄2 tablespoons  chopped fresh thyme
• 1 1⁄2 tablespoons all-purpose flour
• 2⁄3 cup  whipping cream
• 1  cup  fresh breadcrumb, made from crustless French bread
• 1⁄2 cup  freshly grated parmesan cheese

Directions

1. Butter an 8x8x2-inch glass baking dish.
2. Melt 1 tablespoons of butter in a skillet over medium-high heat. Add mushrooms and saute until the juices have cooked away, about 10 minutes. Transfer mushrooms to a large bowl.
3. Melt 1 tablespoons butter in the same skillet over medium-high heat. Add onions and saute until brown and tender, but still holding shape, about 6 minutes. Add to bowl with mushrooms.
4. Melt 1 tablespoons of butter in the same skillet, same heat. Add the brussels sprouts, saute until browned, about 10 minutes.
5. Add 1/2 cup broth to skillet, cover, and simmer until the sprouts are tender, stirring often, about 10 minutes. Uncover and cook until the liquid evaporates, about 1 minute. Add to bowl with mushrooms and onions.
6. Melt 1 tablespoons of butter in the same skillet over medium-high heat. Add garlic and thyme; saute for 1 minute.
7. Add flour and stir for 1 minute.
8. Gradually add remaining 2 cups of broth and cream and bring to a boil, whisking often.Boil until reduced to 1 1/4 cups, about 8 minutes.
9. Mix sauce into the vegetables in the bowl. Season with salt and pepper, and transfer to prepared dish.
10. Note: Can be made 3 days ahead to this point; Cover and chill.
11. Preheat oven to 375°.
12. Melt 1 tablespoons butter in a small saucepan. Mix in breadcrumbs and cheese. Sprinkle the crumb mixture over the vegetables.
13. Bake uncovered until heated through and topping is golden, about 35 minutes.