Salmon in Mustard Gravy

This is an unusual way of cooking salmon that my partner and I discovered (to be honest, he did, I was in fact, sceptical about the whole salmon and mustard combination, but played along anyway) during our MSc course in the UK. We were scouring Sainsbury's for Indian cooking ingredients which also included mustard paste. We didn't find any. The closest we could get was a mustard paste with ale in it, something we weren't very thrilled about. Use of alcohol in cooking is minimal in Indian foods, and judging by our taste buds, we wanted to stay as close to the rules as possible. Yet, the recipe was a success. We still didn't know about wasabi (thanks to our friends Michael Lu for introducing it to us and Kei Kudo for leaving some with us) and we never noticed the Scottish bonnets either. With time we learned about these ingredients and incorporated them, and we stumbled upon a variety of mustard with red chilli flakes and vinegar in it. That was a hit!