Start by heating a large pot of water over med-high heat. Once it comes to a boil, add in the broccoli florets and let them cook for just 3-5 minutes, until crisp-tender. The broccoli will continue to cook in the oven, so this is just to give it a head start. Drain it well and set it aside in a large bowl.

Preheat the oven to 350°F. Line a 9x13" baking pan with foil (for easy cleanup) and grease the foil. Set this aside.

In a medium saucepan, heat the butter over medium heat. Once it's melted and bubbly, whisk in the flour a bit at a time and once it's all added, let it cook while whisking for a minute or so. Then slowly start to add the milk, while still mixing, to form a smooth sauce. Increase the heat to med-high and stir in the seasonings.

Once it starts to bubble, turn the heat back down and let this simmer, stirring often, until it's thickened...about 3-5 minutes.

Once it's thickened up, remove it from the heat and immediately stir in 1 cup of the cheese until it's all incorporated. Then stir in the sour cream.

Toss the broccoli and cheese sauce together in the bowl, then transfer it to the prepared baking pan. Sprinkle the additional cheese over the top, then the crushed up French onions.

Bake uncovered for 25-30 minutes, until it's completely heated through and the broccoli is tender. Serve immediately and enjoy!