POUND chicken breasts to 1/4-inch thickness. Sprinkle evenly with 2 Tbsp. each of the salt and pepper (or 1/2 tsp. of each for the trial recipe). Cover each chicken breast with 2 of the prosciutto slices; set aside.
BEAT cream cheese, blue cheese and parsley with electric mixer on medium speed until well blended. Shape into 48 elongated balls (or four elongated balls for trial recipe), using about 2 Tbsp. of the cream cheese mixture for each ball. Place 1 ball near one of the short ends of each chicken breast; roll up tightly. Secure with toothpicks.
HEAT 3/4 cup of the oil (or 1 Tbsp. of the oil for for trial recipe) in large ovenproof skillet on medium-high heat. Add chicken, in batches. Cook 5 min. or until evenly browned, turning occasionally. Remove from heat; place in single layer in shallow pan.
BAKE at 350°F for 25 min. or until chicken is cooked through (170°F). Meanwhile, heat remaining 3/4 cup oil (or remaining 1 Tbsp. oil for trial recipe) in large skillet on medium-high heat. Add onions, mushrooms and garlic; saute until tender. Add broth and vermouth; cook until sauce is reduced by half, stirring frequently to scrape up browned bits from bottom of skillet. Stir in the cream and remaining 2 Tbsp. each salt and pepper.
REMOVE toothpicks from chicken. Serve each chicken breast topped with 1/2 cup of the sauce.