Preheat oven to 350 degrees. In a small saucepan, sauce onion in olive oil until tender. Stir onions into potatoes, along with milk and 1/2 cup Parmesan cheese. Divide the potato mixture among roast beef slices. Roll up to enclose the potato mixture. Pour 2 Tbsp. tomato sauce in bottom of 3 quart glass baking dish, spread to cover thinly. Place beef rolls in pan, seam side down. Mix diced tomatoes, remaining tomato sauce, basil, salt, and pepper and pour over filled rolls. Cover pan with foil. Bake at 350 degrees for 25-30 minutes, until bubbly. Uncover pan and sprinkle with 1/2 cup Parmesan cheese. Bake 5 minutes or until cheese melts.

To add this recipe to your collection, drag the image to one of your lists in MacGourmet, or right click on it, download the linked file to your computer, and import the file.