HEAT 1 3/4 cups morsels, 1 cup marshmallows and milk in a medium, heavy-duty saucepan over low heat, stirring until marshmallows are melted (do not overheat). Pour into large bowl. Cool to room temperature.
WHIP cream in small mixer bowl until stiff peaks form. Fold 3 cups whipped cream and remaining marshmallows into chocolate mixture. Spoon into crust; swirl top. Garnish with remaining whipped cream and remaining morsels.