In a bowl, sprinkle raspberries with sugar and mash; let stand for 15 minutes. Mash again and strain, reserving juice. Discard pulp and seeds. In a saucepan, combine the raspberry juice, apple juice, vinegar, soy sauce, garlic, and thyme. Simmer, uncovered, for 5 minutes. In a bowl, combine the cornstarch and water. Stir into raspberry juice mixture until smooth. Bring to a boil. Cook and stir for 1 minute or until thickened. Keep warm. Meanwhile, flatten chicken to 1/4-inch thickness. In a large skillet, heat the oil and butter over medium-high heat. Add the chicken; cook until juices run clear. Sprinkle with salt and pepper. Serve with raspberry sauce. Garnish with raspberries and thyme sprigs, if desired. Makes 4 servings.