1) Preheat oven to 400 degrees F.
2) In a medium pot, bring water to a simmer and salt it with a tablespoon of kosher salt. Once simmering, add broccoli florets and cook for 60 seconds until bright green and slightly tender. Drain and rinse with cold water to stop cooking.
3) In a separate smaller pot, combine cream, milk, and stock and heat over low heat until steaming, but don’t boil.
4) In a larger pot, add oil over medium heat followed by onion, garlic, and jalapeno. Cook until soft, about 3-4 minutes. Season with red pepper flakes, salt, and pepper.
5) Add flour to a pot and whisk to stir flour into oil. Cook the roux until it is a light tan color, about 4 minutes.
6) Slowly pour in hot milk mixture, whisking constantly as you add it to the roux base. Whisk well and bring to a slight simmer. The mixture should be the consistency of a thin gravy. If it’s very thin, simmer for a minute or two to thicken.
7) Add grated cheese and stir until cheese is melted. Stir in rice and broccoli. Taste and season with salt and pepper.
8) Transfer mixture to casserole dish and bake for 15 minutes.
9) Top with slivered almonds and return to oven for another 15 minutes.
10) Remove casserole and let cool for a few minutes before serving.