Combine white chocolate and sour cream in a large microwave- safe bowl. Cook on high, for 1 minute, stir. Continue in 1 minute bursts, until chocolate melts and mixture is smooth. Cool.
Using an electric mixer, beat eggs with icing sugar, until pale and very thick. Fold eggs and whipped cream into cool chocolate mixture. Fold in Tim Tam biscuits (reserving 4 biscuits) and raspberries. Spoon into desired glass and top with extra berries and a halved Tim Tam. Cover and refrigerate until firm.