MIX flour and pepper in shallow dish. Add chicken; turn to evenly coat both sides of each breast. Gently shake off excess flour mixture.
MELT butter in large skillet on medium-high heat. Add chicken; cook 10 to 12 min. on each side or until done (165°F). Transfer chicken to platter; cover to keep warm.
ADD tomatoes, tomato sauce and garlic to skillet; cook 3 min. or until heated through, stirring frequently. Stir in broth; bring to boil. Simmer on medium-low heat 3 min., stirring frequently. Whisk in sour cream; cook and stir 2 min. or until heated through. (Do not let sauce come to boil.) Spoon over chicken.