Shepherd’s Pie Casserole

Directions

1. In a large skillet, brown beef, onion and garlic in 2 tablespoons of oil. Add the mushrooms. Cook and stir for 3 minutes; drain. Place the tomato paste in a bowl. Gradually whisk in broth until smooth. Stir in horseradish, mustard, 1 teaspoon salt and pepper. Add to meat mixture. Pour into a greased 11x7-in. baking pan; set aside.
2. In the same skillet, saute the peppers in remaining oil until tender, about 3 minutes. Drain and spoon over meat mixture. Cook potatoes in boiling salted water until tender; drain. Mash with milk, cheese and remaining salt. Beat egg whites until stiff peaks form; gently fold into potatoes. Spoon over pepper layer. Bake, uncovered, at 425° for 15 minutes. Reduce heat to 350°; bake 20 minutes longer or until meat layer is bubbly.