BRING first 6 ingredients to boil in saucepan; simmer on medium-low heat 20 min. or until thickened, stirring frequently. Spread onto bottom of 8-inch square baking dish sprayed with cooking spray.
HEAT oven to 400ºF. Prepare muffin batter as directed on package. Stir in 1/2 cup sour cream; spread over chicken mixture. Top with cheese.
BAKE 20 min. or until golden brown. Serve topped with remaining sour cream.