1. Beat butter in large bowl until creamy. Stir together powdered sugar and cocoa; add to butter mixture alternately with whipping cream and vanilla, blending well. Refrigerate until firm.
2. Shape small amount of mixture around desired center; roll into 36 equal balls (about 1-inch each). Drop into desired coating, turning until well covered. Refrigerate until firm. Makes 3 dozen truffles.
VARIATION: Add 1/2 teaspoon rum extract, decrease vanilla to 1 teaspoon.