Combine the flours, onion powder and rosemary in a large bowl. In another bowl, whisk together the stock, oil, soy sauce, and liquid smoke.

Mix the wet and dry ingredients together to form a cohesive, firm dough. Knead well for 2 minutes until firm, then slice into 8 pieces. Flatten each piece into a fillet with a rolling pin and pound each side as you would with meat.

Heat the stock and soy sauce in a large pot. Add the fillets and cook gently for 30 minutes, ensuring the stock doesn't reach a boil, as this may ruin the seitan's texture. It should barely reach a simmer, especially in the initial stage of cooking.

Drain and dry the fillets on absorbent paper and cool. Coat the fillets in the flour.

Heat glugs of olive oil in an extra-large frying pan. Sear the fillets for a minute on each side, but don't overcook as they will toughen. Remove from the pan. Cook the fillets in batches if necessary.

In the same pan, dry sauté mushrooms on high for a few minutes until they release their moisture. Once most of the moisture is gone, add the butter, garlic and herbs.

Return the fillets to the pan, with the mushrooms. Pour in the wine and simmer until it reduces by half. Add 125 ml of water and cook for a few minutes to thicken. Season with large pinches of salt and pepper to taste.