Spread 1 cup meat mixture onto bottom of 8- or 9-inch square baking dish sprayed with cooking spray; top with layers of 1 tortilla, 1/2 cup meat mixture, sour cream and 1/4 cup cheese. Cover with second tortilla, 1 cup of the remaining meat mixture and 1/4 cup cheese; top with remaining tortilla and meat mixture. Cover.
Bake 25 min. or until heated through. Top with remaining cheese; bake, uncovered, 5 min. or until melted.