Mix the egg yolks with the starch. The mass should be homogeneous.
In a separate saucepan, mix the sugar, milk and cream. Put on medium heat. Stir until the sugar is completely dissolved.
Then, in a thin stream and constantly stirring, pour the warm milk mass into a bowl with the yolks. After that, we return the resulting mass to our saucepan.
Continue stirring at medium temperature. After a while, the cream will thicken. Let the cream mass boil for 1 minute, then turn off the stove.
Add the resulting cold cubes of butter. Stir until smooth.