The vegan butter I use is an organic baking block made from coconut oil. It is hard and you use it straight out of the fridge. Don’t use a margarine or softer butter. It’s a great idea of make the filling the day before so it is cool before using. Leave the Wellington to cool slightly before serving. This will ensure the filling has a chance to firm up. The cooked wellington can be stored in the fridge for about 4 days.