So it turns out making your own mustard is ridiculously easy, though not actually that profitable since mustard powder is not actually that much cheaper than just buying mustard. However, given how easy it is, there's almost no reason not to make it. The main ingredient is yellow mustard seed powder, which you should be able to get almost anywhere. You can also add brown or black mustard seeds (note that they look almost identical), in whole or ground form (I don't see much availability of these as pre-ground, you generally have to grind them yourself). To make the condiment mustard, you'll mix water, vinegar and spices in with your mustard powder/seeds. You then need to wait a couple of days for it to get less bitter - hold in mind while tasting it at first that it's going to be bitter. The main rule of thumb is that the temperature of water you use will play a big role in spiciness - the hotter the water, the less spicy the resulting mustard is. It seems really ...
The Magidow family's modern-day recipe box.