I never cared for storebought mustards. Every time I saw a recipe calling for prepared dijon mustard I'd just say "Blech!" I always thought I just inherently didn't like it. But I got the idea to make this after playing that old school DOS game Legend of Kyrandia 2 where you have to cast the Sandwich Spell. :) In real life, it turned out pretty good after some tweaks and additions. About 1/2 pound radishes/1 large bunch will do it, about 8-10. If buying pre-cut/pre washed radishes-- about 1-1.5 cups should do it. You can use ground mustard powder in place of the seeds if you like, but I like the grainy texture and fresh flavor release the seeds give.