Wash the blueberries, mash them, and rub them through a sieve.
Add lemon juice to the berry puree. Mix the berry puree with the beaten yolks, put the mixture in the freezer for 1-2 hours.
All the ingredients that are added to the parfait must be well cooled, almost frozen, otherwise the parfait will not retain its shape (when mixed, it will “fall off” or even worse, it will curdle …)