THINLY slice boiler potatoes (4 should do it) and layer in 9 x 13 in. pan with sliced onions, mushrooms and ham. Sprinkle with KRAFT 100% Parmesan Grated Cheese and a handful of KRAFT 3 Cheese Blend For Casseroles Shredded Cheese. Repeat layers two more times.
MIX 1 cup each milk and MIRACLE WHIP Salad Dressing until smooth and pour over potato mixture. Sprinkle with additional KRAFT Shredded Cheese to cover top.
BAKE covered in 450°F oven for 50 minutes or until potatoes are tender. Let stand 5 minutes before serving.