Bring 3 cups chicken broth to a boil in a covered pot. While the broth is coming to a boil, start fricassee. Heat a large nonstick skillet over medium high heat. Add oil and butter. When butter melts into oil, add mushrooms and season with salt and pepper, to taste. Cook, stirring frequently, 10 minutes or until mushrooms are all dark and tender. Add vinegar to the pan and stir to coat. The vinegar will cook away in about 1 minute. Add stock to the pan and scallions. Toss to combine.
Stir quick cooking polenta into boiling chicken stock until it masses. Stir in butter and cheese and season with salt and pepper, to your taste.
Serve polenta topped with mushroom fricassee along side sage veal chops or other entree selection.