Combine all the ingredients together. Add the plant-based milk, sugar, potato starch, cornstarch, and seeds from the vanilla bean (slice the vanilla pod in half lengthwise and scrape the seeds) to a saucepan.
Whisk. Next, give it a whisk to dissolve the starches in the milk. Add the vegan butter.
Heat over medium heat. Heat the mixture over medium heat, constantly whisking, until it comes to a boil and thickens. This step will take about 5 minutes.
Transfer to a bowl. Next, transfer the thickened custard to a bowl or deep plate and immediately cover it with plastic wrap touching the top of the cream to prevent it from forming a crust. Let it cool down for about 1 hour at room temperature.
Chill. Before using, I recommend letting the pastry cream cool in the refrigerator for at least 6 hours. It will not only allow it to thicken more but also allow the vanilla to infuse the cream.
