In the past, I have tried using mustard-flavored oil, a blend of regular cooking oil and mustard oil. No wonder my mutschgand did not taste anything like hers. I think I poured most of that oil into my used oil container, and it was eventually recycled.
Pure mustard oil can be found on the shelves of Indian grocery stores, rubbing shoulders with peanut oil, coconut oil and cooking oil. But, according to the FDA, you are not supposed to cook with it. Bengalis, however, have been cooking with it for centuries and are still some of the nicest people I know. So it's not doing anything to their charming disposition, nor is it affecting their intelligence or creativity in any way.