@Mel dCP I used
https://itdoesnttastelikechicken.com/vegan-seitan-steak/
this recipe. It's essentially the same as the one in the Bosh book but they boil theirs in stock. I'd rather steam - keeps the flavour in veg so I've no reason to think it won't do the same here.
I got the vital wheat gluten from Amazon but I know they sell it in the Grape Tree, and probably Holland & Barrett.
I was deeply confused by the carb values given in her recipe but according to this:
https://www.esha.com/how-carbs-are-calculated-in-different-countries/
"Carbohydrate by Subtraction
In the United States carbohydrate is defined as “carbohydrate by subtraction”. This means that when a food is chemically analyzed in a lab, the grams of protein, fat, alcohol, water, and ash are subtracted from the total gram weight of the sample, and the amount left over is considered the carbohydrate value. Using this method, the carbohydrate value contains sugars, starch, and fiber, and may also contain small amounts of other compounds that do not fit specifically in one of the other assays. This carbohydrate definition is used in food composition tables and for nutrition labeling in the U.S. and Canada."
Therefore, I used the British values for insulin calculation and that worked well.