1. Melt white chocolate with 1/4 cup of the whipping cream and the vanilla in heavy, medium saucepan oved low heat, stirring constantly. Pour into 9-inch square pan. refrigerate. 2. Melt semisweet chocolate chips with butter and remaining 1/4 cup whipping cream in heavy, medium saucepan over low heat, stirring constantly. Whisk in liquer. 3. Pour chocolate mixture over refrigerated white chocolate mixture. Refrigerate until mixture is fudgy,but soft, about 1 hour. 4. Shape about 1 tablespoonful of the mixture into 1 1/4 inch ball. To shape, roll mixture in your palms. Place balls on waxed paper. 5. Sift confectioners sugar into shallow bowl. 6. Roll balls in powdered sugar, place in petit four or candy cases( if coating mixture wont stick because truffle has set, roll between your palms until outside is soft. 7. Truffles can be refrigerated 2-3 days or frozen several weeks. Makes about 30 truffles.