Preheat an oven to 400°F and grease a shallow 3-quart casserole dish with butter.
Boil salted water in a large saucepan and cook broccoli cut into 1-2-inch florets until bright green and almost tender. Then remove from heat and cool under cold running water. Dry and set aside.
Take a large saucepan and melt 4 tablespoons of butter over medium heat. Once the butter melts, sizzle it for a minute, and glour and sage.
Whisk in frequently for about 2-3- minutes, but don't let it burn. Then stir in sherry for about a minute and reduce it.
To taste, stir in one cup of chicken broth, milk, heavy cream, nutmeg, salt, and pepper to taste. Bring the mixture to simmer within 6-7 minutes, continuously whisking to remove any lumps.
Stir the Gruyere and scallions into the sauce until they melt and, remove from heat.
Combine sauce, cooked chicken, broccoli, and almonds in a large bowl and pour the mixture over the casserole dish.
Add 1 tablespoon of butter, breadcrumbs, and Parmesan to a small bowl and stir to combine. Pour the mixture over the casserole.
Place the casserole in the oven and bake for about 35 minutes until browned and bubbly.