Mix first 4 ingredients in a small bowl until smooth. Season garlic butter to taste with salt and freshly ground pepper. Melt 2 Tablespoons garlic butter in a heavy large skillet over medium-high heat. Add mushrooms and sauté until all liquid evaporates, about 3 minutes. Add spinach and sauté until just wilted, about 1 minute. Transfer mixture to a medium bowl. Cool 30 minutes. Season stuffing to taste with salt and freshly ground pepper. Place chicken breasts between 2 sheets of waxed paper. Flatten with a meat mallet to ¼-inch thickness. Sprinkle both sides with salt and pepper. Spread 2 teaspoons of garlic butter on one side of chicken. Spoon 2 generous Tablespoons of stuffing onto center of chicken breast. Fold sides of chicken around stuffing, securing with a wooden pick. Place seam side down on a large baking dish. Spread remaining garlic butter over top of each chicken breast. (Note: May be prepared 4 hours in advance. Cover and refrigerate.) Preheat oven to 350º F. Bake until chicken is cooked through, about 30 minutes. Yield: 6 servings. |