In a sauce pan, add the milk, vanilla grains and half of the sugar. Bring to a boil.
In a bowl, mix together the egg yolks and the other half of the sugar until lightened in color. Add the poudre à crème (or corn starch) and mix again.
Once the milk is boiling, pour half of the milk on the eggs, whisking nonstop.
Pour the egg mixture back into the sauce pan and cook on medium heat, whisking continuously.
Once the pastry cream thickens (after about 4 minutes), pour it through a sieve and into the casserole, spreading it out into a thin layer. Cover in plastic wrap, making sure it is in contact with the cream and transfer to the freezer for 10 minutes.
After 10 minutes in the freezer, transfer to the fridge and let it continue to cool.