While the broth heats, whisk together the vital wheat gluten, nutritional yeast, chickpea flour, salt, onion powder, and sage in a large bowl. Make a well in the center and add the 1 ¼ cups broth, soy sauce, and olive oil. Mix with a fork until a dough forms, then knead with your hands for about 3 minutes, until firm and evenly combined.

Divide the dough into 8 equal pieces. An easy way to do this: divide the dough in half, then divide those halves, then those halves again so you have eight pieces. Stretch each piece into a cutlet, pressing it against the counter to smooth the surface.

Once the broth reaches a full boil, lower the heat to a gentle simmer. This part is important: if the broth is at a rolling boil, the seitan can get waterlogged and turn spongy (aka "brains"). Add the pieces of seitan to the pot and partially cover so steam can escape.

Simmer for about 45 minutes, turning occasionally and keeping an eye on the heat to maintain a steady, low simmer- not a boil. When the seitan is done, you can let it cool right in the broth or pull some out to use immediately. For storage, keep the cutlets submerged in broth in a tightly covered container.