Add the soy milk, sugar, cornstarch, and vanilla bean paste to a saucepan and whisk well to remove any lumps. Once whisked, place the saucepan and place on medium heat.
Bring the mixture to a gentle simmer and cook on low-medium heat for about 5 minutes, all while whisking until it thickens enough to coat the back of the spoon.
I recommend that you alternate between using a whisk and a rubber spatula to make sure the custard does not stick to the pan and burn.
The mixture will become thick once the cornstarch is cooked, do not be tempted to over cook it! Remove it once it can coat the back of a spoon, it will thicken as it cools.
Stir in the vegan butter and salt until the butter is melted. Pour into a bowl.
Cover the bowl with clingfilm to prevent a skin from forming and allow the pastry cream to cool for 10 minutes before transferring it to the fridge to cool fully for an hour before using.
Store in an airtight container and refrigerate for up to 5 to 7 days. Use as a filling for berry tart*, raspberry tart**, or choux buns.