Mamie Eisenhower's Favorite Fudge

This is also known as White House Fudge, Mamie's Fudge, Mrs. Eisenhower's Fudge, Million Dollar Fudge and Mamie's Million Dollar Fudge.

1 2/3 cups evaporated milk
4 cups granulated sugar
2 tablespoons butter
2 cups semisweet chocolate pieces
3 (4 ounce) bars sweet cooking chocolate
1 pint Marshmallow Cr