350 grams of whole wheat bread flour
Sea salt, if desired
Put flour in a bowl and add salt if required. Note that 350g flour makes 125g seitan (ish), ie the weight more than halves. 350g is about 12oz (weight not volume) and this is enough for 1-2 servings.
Mix in warm water to make a kneadable dough. Knead for just a few minutes until smooth, the cover with a damp cloth and leave for 30 minutes to 1 hour.
Knead again briefly, then place in a colander under the tap. Turn on the cold water and begin to wash the starch and bran out of the dough, by a combination of kneading and squeezing. Squeeze it inwards to start with - it will seem as though it's going to come apart, but by the time you've finished it will be very reluctant to break into pieces. Swap to hot water after 5 minutes, then alternate with cold every 3 minutes or so. You can mash it down against the colander if this helps.
When the white stuff stops coming out, you've got rid of most of the starch - now for the bran. Scrub as much bran out as possble - if you leave a significant amount in then the result will be inedible (I know this from the one and only time my husband tried this ;-) )
When you've finished, you'll have a tightly-contracted ball of weird stuff. Cut into chunks and simmer in a large pan of stock, seasoned with the stuff you want the seitan to taste of. I use vegetable stock seasoned with garlic, grated root ginger and soy sauce. The seitan will expand - covering the pan will make it lighter and more expanded, whereas leaving the lid off will make it denser. Simmer it until the chunks have risen to the surface and seem cooked - about 5 minutes, but this depends on how much you're cooking at once.