HEAT oven to 350°F.
ARRANGE half the crackers in rows on bottom of 13x9-inch baking dish. Cover with layers of 3/4 cup cheese, sauerkraut and corned beef; top with remaining cheese and crackers.
WHISK remaining ingredients until blended; pour over crackers.
BAKE 40 min. or until top is puffed and golden brown. Let stand 10 min. before cutting to serve.