Preheat Oven to 350 degrees. Melt butter in saucepan over medium heat, add flour and create a roux. Slowly add the broth stirring with a whisk, then the milk creating a sauce. Add the seasonings, 1/4 cup of Reggiano Parmesan and the Sherry. Arrange the broccoli in a single layer in a casserole dish. Sprinkle the remaining Reggiano Parmesan over the steamed broccoli. Top the broccoli with the chicken breasts. Beat the cream into soft peaks and fold into the sauce; pour over the chicken and bake for 30 minutes.