Combine butter and cream cheese in bowl. Beat at medium speed, scraping bowl often, until smooth. Add vanilla; continue beating until well mixed. Beat at low speed, gradually adding powdered sugar, until well mixed. (If mixture is too soft, cover and refrigerate 1 hour or until firm enough to form balls.)
Shape rounded teaspoonfuls of mixture into 1-inch balls. Place onto waxed paper-lined baking sheets. Cover loosely; refrigerate 2 hours or overnight until firm.
Melt chocolate chips and shortening in 1-quart saucepan over low heat, stirring constantly, 3-4 minutes or until smooth. Dip buttercreams into chocolate mixture using fork to turn and remove; let excess chocolate drip off. Place onto waxed paper-lined baking sheet.Garnish with chocolate shavings, chocolate sprinkles and decorator sprinkles as desired.
Refrigerate at least 30 minutes to set.