*To toast coconut in the oven, spread coconut on a baking sheet in a single layer. Bake at 325°, stirring occasionally, until golden brown, about 10 minutes.
In a large mixing bowl, using hands, combine toasted coconut, cookie crumbs, and 1/2 cup of the butter until well blended. Press mixture into a buttered 9-inch pie pan; form a small edge. Cover and chill thoroughly.
In a large saucepan, combine milk, sugar, cocoa, and cornstarch. Bring mixture to a boil over medium heat, stirring constantly, until thickened and smooth. Let mixture boil, stirring constantly, for 2 minutes. Remove from heat; stir in rum and remaining 1/4 cup butter. Pour into prepared chilled pie crust. Refrigerate pie for 2 hours, until set. Serve with whipped cream topping, below.
Whip cream until almost stiff. Add sugar and vanilla; beat until cream holds peaks. Spread over top of cooled pie or use as a dessert or shortcake topping.