Put the whisk & metal bowl in the freezer to chill until later.
Soak the gelatin sheets in cold water for 15 minutes
Prep a shallow casserole with plastic wrap. Overlap two sheets of plastic wrap leaving excess on both ends, so you can cover the cream afterwards.
In a sauce pan, add the milk and half of the sugar. Add the vanilla extract or vanilla grains/bean. Bring to a boil.
In a medium sized bowl, add the egg yolk and remaining sugar. Whisk until combined and lightened in color.
Add the crème à poudre or corn starch and whisk until combined.
When the milk comes to a boil, take off the heat and discard the vanilla bean. Pour 1/3 of the milk on top of the egg mixture, whisking constantly. This tempers the mixture.
Pour the egg mixture into the saucepan with the remaining milk, whisking non-stop.
Turn the heat back on to medium and continue to stir without stopping. After a couple minutes, the cream will start to thicken. Add the gelatin and whisk until dissolved.
Continue to cook for an additional 3 minutes, then strain the cream into the casserole.
Let cool for a couple minutes, then fold in the excess plastic wrap over the cream, making sure it's in contact with the cream (this will keep it from creating a crust). Transfer to the freezer for 10 minutes, then move to the fridge to continue cooling for about another 30 minutes.
Once the pastry cream has cooled, transfer it to a bowl and whisk it until it has loosened up and smooth.
In the chilled mixing bowl, add the heavy cream and whip until you have a semi stiff peaks.
Add 1/3rd of the whipped cream to the pastry cream, gently folding until fairly well combined. Continue with another third of the whipped cream then finish off. Fold until thoroughly combined and smooth.