Bring a pot of water to a boil and cook noodles as directed on their package. Toss in broccoli florets for the last 3 minutes of cook time. Drain and set aside.
While the pasta is cooking, start making the base of the sauce, the roux. Melt butter then add spices and flour until it thickens. (I like to make this in a large, oven-safe skillet so I can go right into the oven with it.)
Cook for about 5 minutes to cook off the flour taste.
Slowly add in milk, then stock and cook until it thickens into a sauce. (About 5 minutes.) If there are large chunks of flour, whisk until they dissolve.
While the sauce thickens, preheat the oven to 350°F.
When the sauce has thickened, stir in the cheese until it melts.
Now, mix in the cooked noodles and broccoli along with the diced chicken.
Mix in crispy onions if desired.
Pour the sauced chicken mixture into a 13 x 9 baking dish or bake in the skillet you are working in (if it is oven-safe.)
Bake for 15 minutes.
While the casserole is baking, melt butter and mix with remaining crispy onions and panko breadcrumbs.
After 15 minutes, remove the casserole from the oven and stir it really well. Then top with breadcrumb mixture and bake for 7 more minutes. (22 minutes total.)
Remove from oven and let the casserole cool a little. Serve and enjoy!