Heat oven to 350°F. Spray 8 (10-oz) ramekins or custard cups with cooking spray. Place ramekins on large cookie sheet with sides. In 12-inch nonstick skillet, melt 2 tablespoons of the butter over medium-high heat. Add chicken; cook about 10 minutes, stirring occasionally, until no longer pink in center. Remove chicken from skillet; discard chicken juices.