Preheat oven to 400 °F (200°C).

To a food processor add everything except the vital wheat gluten. Process until pretty much smooth. You will still see some little tiny lumps of black beans in there and that's fine. If you don't have a food processor you can do this in a blender instead.

If you used a food processor, add the vital wheat gluten to the food processor and process for a minute or so until a ball forms. Once you see the ball flopping around inside, turn off the food processor. If you used a blender instead of a food processor, pour the blended mixture out and into a large mixing bowl, making sure to scrape every last bit out with a spatula, then add the vital wheat gluten. A blender won't be able to handle the dough. Give it a good stir to combine everything then bring it together into a dough with clean hands.

Tip the dough out onto a clean surface and knead for 4 minutes (5 minutes if you did not use a food processor to make the dough). I find that I don't need to flour my surface, but if it gets a little sticky you can sprinkle a little vital wheat gluten on it to make it easier. As you knead you will feel the dough getting tougher to handle and visibly see it becomes more fibrous.

Shape the dough into a log shape roughly 8½ inches long and 4 inches wide.

Cut a generously sized piece of foil (about 20 inches long) and grease the centre of it (where you'll sit the seitan) lightly with some oil. Pick up your seitan and put it in the middle of the foil then wrap it thoroughly but not too tightly as it will expand as it cooks. Try to have all edges sealed up so it traps the steam in as it cooks. Once done, wrap it again in another piece of foil. This protects it and stops it getting too brown while baking.

Sit the wrapped seitan on a small baking tray and place in the centre of the oven. Bake for 70 minutes, flipping once half way through the cooking time.

Leave in the foil and allow to cool. Seitan is best and meatier, when made in advance and refrigerated overnight.