5 tablespoons unsalted butter, plus more for the dish
Kosher salt
1 large head broccoli, cut into 1- to 2-inch florets, tender stems peeled and cut into 1/2-inch slices (about 5 cups)
1 tablespoon chopped fresh sage
5 tablespoons all-purpose flour
3 tablespoons dry sherry (or chicken broth)
1 cup low-sodium chicken broth
1 cup milk
1 cup heavy cream
Pinch of freshly grated nutmeg
Freshly ground pepper
1 bunch scallions, chopped (about 1 cup)
1 1/2 cups shredded gruyere cheese (about 6 ounces)
1 cooked 3 1/2-pound chicken, meat removed and cut into chunks, skin and bones discarded (3 to 3 1/2 cups meat)
1/2 cup sliced or slivered almonds, toasted
1/2 cup grated parmesan cheese
1/4 cup breadcrumbs