Fold in egg whites. Pour batter into pan. Bake 20 mins or until a toothpick inserted in center comes out clean. Let cake cool. In bowl, beat remaining butter and vanilla. Beat in powdered sugar and then the marshmallow fluff. Poke holes into the cooled cake and pour the chocolate syrup over the holes, smoothing the syrup out as you go. Frost the cake w/ the marshmallow mix. Sprinkle the top of cake w/ remaining cracker crumbs. Drizzle w/ chocolate syrup. Dig in!!