Melt chips with whipping cream in heavy, medium saucepan over low heat, stirring occasionally. Whisk in rum extract and vanilla until blended. Pour into pie pan. Refrigerate until mixture is fudgy, but soft, about 75 minutes. Shape about 1 T into 3 cm ball. To shape, roll mixture in your palms. Place balls on waxed paper. Sift powdered sugar and cocoa into a shallow bowl. Roll balls in sugar-cocoa mixture; place in petit four or candy cases.