Blitz the tofu, soy milk, miso, Marmite, onion powder, garlic powder, 1 tsp salt and ½ tsp white pepper in a food processor until smooth.
Tip into a bowl and add the wheat gluten and pea protein or protein powder. Mix to form a dough. Once the dough has come together, give it a really good knead, stretching and tearing for 10-15 mins. It will be ready once the dough feels springy.
Pour the vegetable stock into a pan. Bring to a simmer. Flatten out the seitan to a thickness of 1cm and chop into chicken-breast-sized chunks. Simmer these in the stock for 20 mins, covered with a lid, then allow to cool in the stock. Ideally, do this the day before and leave to chill in the fridge. The seitan chunks can also be frozen if you wish. When you’re ready to use the seitan in a recipe, pat it dry with kitchen paper then chop or tear into smaller pieces before cooking, if you like.