Stir the gelatin in water in a small bowl and let it rest and swell (bloom) for about five minutes while you continue with the recipe.
Bring the milk to a simmer in a small saucepan.
While the milk warms up, stir together the egg yolks, sugar and vanilla in a medium bowl.
Temper the egg mixture by pouring some hot milk in, stirring constantly. Then, pour in the rest of the milk.
Return this mixture to the saucepan and thicken on medium-low heat. It should take about 5 minutes.
Remove the custard from the stove and stir in the bloomed gelatin until it is fully dissolved.
Let the custard cool. It should have the consistency of heavy cream.
Once the custard has cooled (but not set!) for about 15-20 minutes, divide between the 4 crusts.
Place in the fridge to rest.
After 10-15 minutes, drop about 1/2 cup of pomegranate seeds on top of each tartlet, pressing LIGHTLY on top of the custard. Place the seeds on top of the custard one pinch at a time in order to not disturb the custard or cause the seeds to bleed!
Let the tartlet set completely in the fridge for a minimum of 2 hours.
Serve at room temperature.