Double Chocolate Squares

Line a 8-inch square pan with heavy aluminum foil. In a small bowl, combine white chocolate chips and 1 tablespoon butter. Microwave on high for 1 minute, or until melted and smooth when stirred. Pour half into the 8-inch pan. In another bowl, combine cream and 2 tablespoons butter. Microwave on high just until the mixture begins to boil. Stir in semisweet chocolate chips and mix until melted. Stir in vanilla. Pour into the pan on top of the vanilla and chill for 10 minutes. Microwave the remaining white chocolate mixture until soft and pour on top of the chocolate mixture. Cut into 1-inch squares, cover, and chill until firm.