Chocolate Rum Mousse Pie
["1 tsp. unflavored gelatin", "1 Tbsp. cold water", "2 Tbsp. boiling water", "1/2 c. sugar", "1/3 c. Hershey's European style cocoa", "1 c. (1/2 pt.) cold whipping cream", "1 tsp. vanilla extract", "1 baked 8 or 9-inch pie crust, cooled"]
["In small cup, sprinkle gelatin over cold water; let stand 1 minute to soften.", "Add boiling water; stir until gelatin is completely dissolved and mixture is clear.", "Cool slightly, about 5 minutes."]
["unflavored gelatin", "cold water", "boiling water", "sugar", "cocoa", "cold whipping cream", "vanilla extract", "pie crust"]