In a bowl, combine the sugar, cornflour, custard powder and salt.
Gradually whisk in a small amount of the cold soya milk to form a smooth, lump-free paste.
In a saucepan, gently heat the remaining soya milk with the plant cream and vanilla over medium heat. Do not boil.
Pour the slurry into the saucepan, whisking continuously.
Cook over medium heat, stirring constantly, until the mixture thickens to a smooth, glossy custard (similar to pastry cream).
Continue cooking for 1–2 minutes to remove any starchy taste.
Add in the vegan butter until fully incorporated.
Divide evenly between 6 ramekins. Tap lightly to remove air bubbles.
Refrigerate for at least 4 hours, preferably overnight, until fully set.
Sprinkle a thin, even layer of demerara/caster sugar mix over each custard.
Using a blowtorch, caramelise the sugar until golden and glassy.
Allow to set for 1–2 minutes before serving.
