We buy potatoes in bags of 1kg and when the two of us eat them, e.g. with Raclette, there are always a handful of leftover cooked potatoes. I used to chop them into the next salad but lately I’ve begun to mash them up and put into the sourdough bread. When I make bread I use 300g spelt flour, or maybe 250g spelt and 50g whole wheat etc. Using 300g spelt and 1 mashed potato gives excellent results. I also tried more potatoes but then the bread falls apart.