Prepare: Make the vegan mascarpone the day/night before. Prepare the vegan ladyfingers - this can be done on the day (recommended), or a day ahead of making the tiramisu.

Make the vegan sabayon: Add the soy milk, rum, sugar, cornstarch, and vanilla extract to a heavy-bottomed saucepan and whisk well until smooth without any visible lumps.

Bring to a simmer over low-medium heat while continuously whisking. Cook for 3-4 minutes until you have a very thick custard.

Remove the saucepan from the heat. Add the cold cubed butter to a large mixing bowl and pour the hot custard on top. Whisk vigorously until emulsified.

Cover the sabayon with plastic wrap and place it in the fridge to chill completely for 30 minutes to an hour.

Make the mascarpone cream filling: Once chilled, add the vegan mascarpone to a blender jug and scoop the sabayon mixture on top. Blend until smooth and creamy.

Make the espresso soak: In a wide shallow bowl or container, mix together room temperature espresso and rum, set aside.

Assemble: Add a thin layer of the mascarpone cream to the base of a dish. Individually dip each ladyfinger in the rum-espresso soak for 2-3 seconds on each side and arrange them on top of the cream.

Divide the remaining vegan mascarpone cream into 2 parts. Smooth out one part on top of the ladyfingers. Repeat with a second layer of soaked ladyfingers.

Spread the remaining mascarpone mixture on top and smooth it out.

Dust unsweetened cocoa powder on top of the final layer of mascarpone. Refrigerate the tiramisu until set for at least 4-6 hours (overnight for best results).

Serving: Mark out servings with a sharp knife and use a wide metal spatula to lift out the slices.

Storage: Store in the refrigerator until serving. Cover tightly with plastic wrap. It will keep in the fridge for 4 days.