Heat oven to 400°F Spray 8-inch square (2-quart) glass baking dish with cooking spray.
In medium bowl, stir Bisquick mix, milk, egg and 1 teaspoon of the caraway seed with fork until blended. Spread 1 cup batter in baking dish.
Brush corned beef slices with mustard; layer on top of batter in baking dish. Top evenly with cheese and sauerkraut. Carefully spread remaining batter over sauerkraut. Sprinkle with remaining 1 teaspoon caraway seed.
Bake uncovered 28 to 32 minutes or until light golden brown and center is set. Let stand 5 minutes before cutting. Serve with Thousand Island dressing.