Preheat oven 325°F (or 300°F if using a dark, nonstick springform pan) Crust Mix: crumbs, 3 Tbsp. sugar, and butter. Press in bottom of 9 inch springform pan. Bake for 10 minutes.
Filling: Mix cream cheese, 3/4 cup sugar, and vanilla with mixer. Add eggs one at a time. Stir by hand each 1 cup chocolate and marshmallow. Then pour filling over crust. Sprinkle with remaining 1/2 cup chocolate and 1 cup marshmallows.
Bake 50-55 minutes or until center is almost set. When done, run a knife around rim to loosen cake. Refrigerate 4 hours or overnight.