Preheat oven to 350 degrees.
In medium bowl, beat egg yolks until pale yellow. Add the heavy cream.
Temper the egg yolks by adding 1/3 cup of egg custard to the butterscotch sauce and whisk. Then add the rest of the butterscotch sauce. Mix well and pour into 4 ramekins, about 2/3 full.
Place ramekins in large baking dish with sides. Pour hot water around ramekins about 2/3 up the sides.
Bake 35-40 minutes. Remove from heat and allow to cool. Refrigerate until ready to use.