In a double boiler, mix in the sugar, cornstarch and salt. Then gradually stir in the milk and cream mixture.
Cook covered over hot water for 8 minutes without stirring. Uncover and cook for about 10 minutes more.
Add the egg yolks and butter. Cook and stir these ingredients over hot water for 2 minutes longer.
Cool, stirring occasionally to release steam, then add the vanilla.
Fold in the whipped cream. Chill the custard. It will have the consistency of a heavy whipped cream.
For white chocolate whipped cream:
Place 1 cup whipping cream into an electric mixer. Mix until whipped. Fold the whipped cream into 1/2 cup of white chocolate sauce.
Brush the ladyfingers generously with creme de cacao and white wine. Arrange a dense layer of ladyfingers on the bottom of a trifle bowl.
Pour on half of the jar of chocolate sauce. Add half the custard.
Then brush the next layer of ladyfingers again with the creme de cacao and white wine. Arrange the ladyfingers on top of the custard.
Pour on the last half of the sauce. Add slightly half the berries in a layer. Top with remaining custard.
Add another layer of ladyfingers, brushed with the wine and creme de cacao. Add the white chocolate whipped cream onto the ladyfingers. Arrange the remaining raspberries around the edge. Place the entire dish in the refrigerator to chill.