Cheesy Bacon Green Bean Casserole

Preheat oven to 350 degrees (F). Lightly grease a 9x13-inch casserole dish and set aside. 
Trim the rough ends of the green beans and cut them in half, if desired. Set aside.
Bring a large pot of lightly salted water to a rolling boil. Blanch the green beans by dropping them into the boiling water and allowing them to par-cook for 4 minutes.
Using a slotted spoon, remove them from the boiling water and immediately plunge them into an ice bath to stop the cooking process. Drain the green beans once they're cool, then pat them dry. Place them in the prepared baking dish and set aside. 
In a large skillet over medium-heat, cook the bacon until crispy on both sides, about 4 to 5 minutes per side. Remove from heat and place on a paper towel lined plate. Blot any excess oil with a paper towel, then chop into small bits. Set aside. 
Drain skillet of any excess bacon grease, then place back over medium-heat. Add the butter and swirl to melt. Add in the chopped onion and cook, stirring frequently, for 4 to 5 minutes, or until softened and nearly translucent. Add in the garlic and cook, stirring constantly, for 1 minute.
Sprinkle in the flour, and stirring constantly, cook for 1 minute. Slowly pour in the milk and then the broth, stirring constantly as you add. 
Cook, stirring constantly, until the mixture begins to thicken, about 2 minutes. Stir in the brown sugar, salt, pepper, and cayenne pepper. 
Remove the pan from heat. Immediately stir in the heavy cream, then add the cheddar, Monterey Jack, and parmesan. Fold in half of the chopped bacon and half of the French fried onions. 
Pour sauce over green beans and stir gently to combine. Bake for 25 minutes. Then top with remaining bacon and onions and bake for an additional 5 minutes. Serve warm!