In a large bowl, mix the erythritol, egg yolks, arrowroot and salt together. You'll get a light yellow creamy paste.
In a small pot, pour in the heavy cream and heat on medium heat until it starts to bubble. Once it bubbles, turn off the heat.
Take one cup of hot cream and slowly pour it into the egg yolks mixture. Mix to combine. Once the milk has been added, pour the egg mixture into the leftover cream in the pot, add the vanilla and mix to combine again.
Set the pan back over medium heat. Whisk constantly. The pastry cream will start to look thin and frothy, but eventually it'll start to thicken after a couple of minutes. Once its thickened to a pudding consistency, turn off the heat immediately. If your heat is too high, or if you don't whisk consistently, you might break your custard. If that happens, see notes above to see how to fix a broken pastry cream.
Transfer the pastry cream into a strainer to sieve it. This will get rid of any bumps it may have and make it extra smooth.
Cover with saran wrap, let it cool down to room temperature and then cool it into the fridge until ready to serve.
The nutritional information is for 2 cups of pastry cream. Feel free to cut it and calculate it for how many portions you want to make.