Place potatoes in large saucepan with just enough water to cover. Bringto a boil and cook 15 minutes, or until potatoes are tender.

Drain potatoes. When cool enough to handle, peel and grate.

In large bowl, mix melted butter, beaten egg, and parmesan cheese. Stirin grated potatoes until well-blended.

Preheat oven to 350 degrees. Lightly coat interior of cups of a 12-cup muffin tin with cooking spray.

Press grated potato mixture in bottom and up sides of muffin cups.

Divide mozzarella cheese evenly between muffin cups. Top cheese with a tomato slice. Place a basil leaf on top of each tomato slice.

Bake 20 minutes, or until tomato slices are cooked and cheese is golden-brown.