Preparation: Preheat the oven to 275 degrees. Pour butter into a 13x9 dish and coat the bottom and sides.
Bread Pudding: Heat the cream in a double boiler and add the white chocolate. When the chocolate is melted, remove from heat and set aside.
In a double boiler, heat the milk, sugar, eggs and egg yolks until warm. Blend the egg mixture into the cream and chocolate mixture.
Place the bread slices in a baking pan. Pour 1/2 of the mixture over the bread and let settle for a while (about 20 minutes), making sure the bread soaks up all the mixture. Top with the rest of the mixture. Cover with aluminum foil and bake for 1 hour. Remove the foil and bake for an additional 15 minutes until the top is golden brown.
For the sauce: Melt the white chocolate in a double boiler over barely simmering water. Remove from heat and mix in heavy cream. Spoon over bread pudding.