It's easy to make and quite honestly the hardest part is finding the mustard powder and mustard seeds to make it with. I get mine from Penzey's. Here's a link to their mustard offerings. While you're there, take a look around at the other fabu things they offer.
So here's the thing about mustard. It can get really hot. I'm not all that big on 'really hot', so I like to dial it down a bit. Which means you need to know about how mustard chemistry works. These are the basics:
Mustard gets hotter, the more you expose it to the air. This means that mustard powder is way hotter than mustard seeds.
Mustard made with water is hotter than mustard made with vinegar [vinegar is acid]. It's a chemistry thing. See the very top link for a post with other links to more specific information.
Once the mustard is made, it will tone down if you leave it out of the fridge in the cupboard to meld for a few weeks. Or months. We tried it, it works. We left last year's mustards out for 6 months and it got mellower and mellower without a trace of mold or anything nasty.
So, if I want milder mustard, I want to do it by grinding seeds in vinegar.
If I want a hot mustard, then I use mustard powder in water.
I fear I wasn't very pleasant about it. Seriously. Food processors have one job. To process food. Apparently our food processor wasn't aware that mustard seeds and vinegar are food. Arg.
Since I was doing a small amount, I didn't want to put it in the blender because I would have lost too much to the sides of the canister, but I'm guessing the blender would have worked just fine.
Nooo, I decided to put it in my mortar and pestle and grind them by hand. How hard could it be? Plus, then it would be all Stone Ground.
I thought I was so cool.
Instead of going around and around, the mustard just went up and down. So I covered it all with plastic and left it over night. The next morning, it actually started grinding. Sort of. So I ground it for a while, then left it until that night.
Once the seeds started really softening, they started grinding a lot better. Then the mustard started seriously soaking up the vinegar, so I added another part of vinegar.
We mortared. We pestled. We mortared again. We pestled again. Then I wrapped it up and left it overnight. Again.
The next day it was much much softer but still way too rough. Grinding with the mortar and pestle was working, but too slowly. I pulled out the stick blender and used that until I was able to get it ground to a great rough consistency that I really like.
We tasted it and it is delicious! Thank heaven. It still has a good mustard kick, but is much milder than the ones we made last year.
If you try mustard this way, try it in a blender first. Better yet, soak the seeds in the vinegar for a day before you start grinding at all. These are the proportions I ended up with to get the consistency I like:
Homemade Mustard [Mild-ish]
1/4 cup yellow mustard seeds
1/2 cup white wine vinegar
Grind the mustard seeds with the vinegar until you reach the consistency you like. Store in fridge to maintain that heat level. Store in cupboard for a milder mustard [after a few weeks or months.] Makes 3/4 cup.