I would use mustard seeds that you pulverize/grind into a powder in a grinding bowl (like a suribachi or a mortar) with a pestle. Because commercial mustard is often cut with flour (and I'm gluten-free) I don't keep dry mustard around, but I do keep mustard seeds in the freezer for when I do need dry mustard and mill it fresh. It's also more potent (hot) than commercial dry mustard, so you may not need to use as much.

Be VERY careful if you mill mustard seed in a coffee/spice mill. "The substance that makes mustard hot—allyl-isothiocyanate—will irritate your eyes and nose if you get too close. When mustard seeds are crushed and mixed with water, they release volatile oils which act like capsai­cin, the hot component of chile peppers."

FYI - it won't be as dark as commercial dry mustard because after they cut it with flour they add some turmeric to give it some color, which you could also do, if you want more color.

-Grainlady

Grainlady, thanks! I don't have mustard seeds. I'm wondering whether half tsp dry mustard equals 1 tsp prepared mustard? Or would it equal 2 tsps??

One tsp Colemans flour is about 1tbsp prepared. Mustard seed, flour, powder expands about 5x in liquid.

You can use your prepared mustard. Just start with a tbsp but might need 2.

Just taste before adding too much. Prepared mustards will have various additions like vinegar, sugars, wine, turmeric, etc. You might even prefer it.

Mustard powder/flour absorbs a lot of water so using Colemans will suck up the vinegar...adding prepared mustard will be adding a bit of liquid. Your salad will just be a bit wet. Probably not that noticeable unless you cut back a bit on the ac vinegar.

I stock seed and make my own mustards. Not easy getting as fine a grind as the Colemans flour. It is pure ground seed, not 'flour' as in grain. (unless they are liars, lol)

All true about the grinding 'irritant'. Instead i soak my seed to soften, cold water 1/2 hour then add vinegar...24 hrs, then grind in a high speed blender. Cuts way back on the irritants.

For the future, If you like the original Colemans you can order from Amazon. Good pure mustard flours out there. Just avoid the 99cent brands no mater what the label says as they most likely have fillers.

Thanks sleevendog! I'll do as you suggested. You replied just in time before it was too late. Saved my salad!

Since I believe the recipe originally came form me....I am chiming in to tell you that you sure can substitute a prepared Dijon mustard for Coleman's powder.
I've done it when I have been out of Coleman's dry> And I use about a tablespoon of the prepared.....enough so you get some mustard bite!
I am about to make that recipe times 15 for a church dinner!!

Absolutely you can sub prepared mustard. Looks delicious!

I certainly didn't know that flour was mixed in with ground mustard. I did check a pkg at the store this morning, and it 'could' contain peanuts and other nuts and wheat.

The only other kind of dry mustard was Keen's and there was no ingredient list to be found anywhere on the can.

Fred Harvey was the guy who made railroad journeys in the American West comfortable, way back when. He opened the Harvey House restaurants, along with other hospitality businesses, in or near the train stations, catering to everybody with a few dollars, rather than just the wealthy. I'm thinking that might bear on why the recipe specifies dried--much easier to ship and store. :) Because, like everyone else, I agree that you can substitute prepared in a salad dressing. :)

Many thanks to all of you! It was a hit.

One guest left with what was left from the slaw (I also served an Italian baked beetroot salad, so some slaw survived). The other guest asked for the recipe.

Very interesting, plllog, about Fred Harvey. I enjoyed reading that sidenote.

Fred Harvey was out to make a buck. He knew that coach passengers on the trains were hungry when the train stopped, and rushed to fine a good sandwich shop. So he built good clean standardized restraunts as close to the train station as he could and manned them with "Harvey Girls"...clean cut looking girls who wore a uniform and were held to strict standards. His menus were uniform and you knew what to expect at a Harvey House And he succeeded and built more restaurants. he was the Howard Johnson of the rail roads; he created the first chain of restaurants. After he died his sons and grand sons carried out his legacy.

I have a very similar recipe and I use regular salad mustard all the time.