Put the milk with the scraped vanilla pod in a small saucepan, and bring it to a boil.
Remove the pan from the stove and filter the milk.
Separately, in a bowl pour the egg yolks, the vanilla caviar, sugar, and the grated zest and whisk vigorously until completely combined.
When the mixture is blended, add the corn starch sieved in, stir well to incorporate it.
Pour the milk into the mixture of egg yolks, sugar, and corn starch.
Put on the stove and stir constantly with a whisk (the egg begins to coagulate at 52 °C (125.6°F) temperature; the cooking is complete at just 67°C (152.6°F).
If it is cooked too much, the cream will have a strong smell of egg.
Remove the cream from the stove as soon as it starts to thicken.
Cool it quickly by pouring it into a cold pan and continue to stir with a whisk bringing it to a temperature below 50°C (122°F), this allows it to maintain the consistency of the cream intact.
The pastry cream would be ready for use; otherwise cover with plastic wrap in contact with the surface of the cream, let it finish cooling at room temperature, and then refrigerate.