Place the white chocolate chips or chunks in a blender.
Put the egg yolks in a medium-sized bowl. Whisk in the sugar. Have the bowl and the whisk near the stove so you can use both when tempering the eggs.
Heat the cream in a saucepan over medium-high heat until it is scalded. It takes about 5 minutes.
Once the cream is scalded and has risen in the pan, turn the heat down. Add a ladle full of cream, about 2 ounces, to the egg yolks. Whisk in the cream into the eggs. Add another ladle full of cream and whisk in. Do this procedure a total of three times. The idea is to bring the eggs to temperature slowly so that you don't scramble them.
Add the cream/egg mixture back to the pan, stirring everything together. I like to use a spatula for this step. Increase the heat to medium. Continue stirring with the spatula and heat the cream and egg yolks until they start to thicken. This takes about 3 minutes. Do not cook too long and the cream and eggs are too thick. The eggs will be scrambled.
Add the hot cream mix to the blender, pouring over the white chocolate. Do not let the cream sit in the hot pan, as it will continue to overcook the eggs. Process in the blender for 1 minute. The chocolate should be melted and incorporated with the cream and eggs.
Let the mix cool for about 30 minutes. Add 3 tablespoons of sparkling wine or champagne to the white chocolate. Mix completely.
Pour 6 ounces of pot de creme mix into each of your dishes. Place the filled dishes in the refrigerator for at least 2 hours for the pot de creme to set up. Garnish with the sugared champagne grapes.