(adapted from The Gourmet Cookbook)
1 1/4 lb. skinless, boneless chicken breast halves, rinsed and patted dry
salt and freshly ground pepper
1 T. olive oil
1 1/2 lb. broccoli, trimmed and cut into 4-inch florets
4 T. unsalted butter, cut into pieces
5 T. all-purpose flour
2 c. chicken stock or low-sodium broth
1/2 c. heavy cream
1/4 c. medium dry sherry
2 t. fresh lemon juice
1 c. finely grated Parmigiano-Reggiano
Season chicken with salt and pepper.
Heat oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking.
Add chicken and cook, turning once, until cooked through, about 8 - 12 minutes.
Let stand for 5 minutes, then cut into thin slices.
Meanwhile, cook the broccoli in a large pot of boiling well-salted water until just tender, 6 to 8 minutes; drain.
Preheat oven to 375 F.
Melt butter in a heavy saucepan over moderately low heat.
Add flour and cook, whisking, for 3 minutes.
Add stock in a slow stream, whisking constantly, and bring to a boil, whisking.
Reduce heat and simmer, whisking occasionally, for approximately 20 minutes more.
Remove from heat.
Beat cream with an electric mixer until it holds stiff peaks.
Fold cream into sauce, along with sherry and lemon juice.
Stir in 1/4 t. salt and 1/8 t. pepper.
Arrange broccoli evenly in bottom of a 2-quart gratin or other flameproof shallow baking dish.
Pour half of sauce over broccoli.
Stir 1/2 c. Parmesan into remaining sauce.
Arrange chicken over broccoli, and pour remaining sauce over chicken.
Sprinkle with remaining 1/2 c. Parmesan.
Bake until just hot, about 15 minutes.
Turn oven to broil, and broil about 5 inches from heat until sauce is golden and bubbling, about 1 minute.