Au Gratin Potatoes: Coat 3 half-hotel pans (or 1 half-hotel pan for trial recipe) with cooking spray. Pour 4 oz. bechamel sauce into each prepared pan; top with 14 oz. potato slices| overlapping to make even layer. Cover with remaining sauce.,Sprinkle 1 cup cheese over sauce in each pan| then drizzle 1/4 cup milk along sides of pan to moisten. Cover with foil. Bake in 350ºF convection oven 15 min.,Remove foil. Bake potatoes additional 3 to 5 min. or until bubbly and browned. Cut potatoes in each pan into 4x2-1/2-inch rectangles.,For each serving: Season 1 steak with salt and pepper. Grill to desired doneness. Top with 1 oz. steak sauce and 1 potato rectangle. Serve over bed of 4 grilled scallions.