Step 1
Heat butter and oil in a skillet over medium heat. Add onions and mushrooms. Cook and stir until very brown 10 to 15 minutes. Drizzle truffle oil on top and season with salt and pepper. The filling should paste-like. Set aside to cool while you make the seitan.
Step 2
Measure vital wheat gluten into a large bowl. Add garlic powder onion powder and lemon-pepper seasoning.
Step 3
Mix cold water and wine together in a separate bowl. Stir in molasses and liquid smoke until dissolved. Add liquid mixture to vital wheat gluten and stir to a dough-like consistency. Separate dough into 2 rolls and knead each for a few minutes until dough feels similar to pizza dough. Stretch each portion into an 8x10-inch oblong being careful not to create holes in the dough.
Step 4
Spread cooled mushroom mixture equally onto each dough oblong and roll up tightly like a jelly roll. Wrap each roll with aluminum foil and twist ends closed tightly.
Step 5
Place a steamer insert into a large saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add aluminum-foil-wrapped seitan rolls cover and steam for 1 hour.
Step 6
Preheat the oven to 350 degrees F (175 degrees C).
Step 7
Unwrap steamed seitan rolls and place in a roasting pan. Baste with olive oil.
Step 8
Bake in the preheated oven until browned about 20 minutes.