Immediately add the lemon juice, broth, and the remaining 2 tablespoons butter.
Place the chicken and mushrooms in the pan, cover, and simmer 10 to 15 minutes. Add the capers and cook covered 2 to 3 minutes. Remove the chicken to a platter and keep warm in a 175-degree oven. To thicken the sauce (if desired), add a dusting of flour and whisk until smooth. Increase the heat and simmer briskly to reduce the liquid and concentrate the sauce.
Serve with: green vegetable or tossed green salad, plus fettuccine or rice. If you serve fettuccine, sprinkle the cooked pasta with a little olive oil, fresh Parmesan cheese (see Note, p. 67 of first book), and fresh parsley.
Variation: Replace the chicken with fish, such as tilapia or halibut.