Cream the butter, add pepper, parsley, onion, garlic, and lemon juice. Split a young chicken as for broiling, place in dripping-pan, sprinkle with salt and pepper, dot over with butter, and bake in a hot oven until nearly cooked. Butter plank, arrange a border of Duchess Potatoes close to edge of plank, and remove chicken to plank. Clean, peel, and sauté mushroom caps, place on chicken, spread over prepared butter, and put in a very hot oven to brown potatoes and finish cooking chicken. Serve on the plank.