Broccoli & Gruyere Gratin

2 large bunches broccoli, roughly chopped

1/2 stick butter

1/4 cup flour

2 cups whole milk

2 cups grated Gruyere

S&P

Heat oven to 375. Steam broccoli until just tender. Melt butter in saucepan over medium heat. Add flour and cook (stirring) for 2 minutes. Whisk in milk and simmer until slightly thickened, 3-4 minutes. Remove from heat and stir in 1 cup of cheese, 1/2 tsp. salt and 1/4 tsp. pepper. Toss in broccoli. Transfer to shallow 3-quart baking dish and sprinkle with remaining cheese. Bake until bubbling, 35-40 minutes. Let sit 10 minutes before serving.