Homemade Grainy Mustard

I've been very frustrated reading instructions for making mustard on the internet.  Some call for cooking it, others say never heat mustard.  Some say it gets stronger with sitting, others that it mellows.  I'm currently guessing that it gets stronger when you grind it until you add vinegar, then mellows, at least so long as it is at room temperature.  So here is my first try, rather randomly put together from various recipies I read.  My goal was a mustard with a lot of mustard flavor but not a lot of hotness.  I didn't measure anything, so amounts are approximate.

1 cup yellow mustard seeds
1/4 cup brown mustard seeds
pure cold water to cover by an inch
1 tblsp sea salt
1/4 cup cider vinegar
2 tblsp whey from yogurt or kefir

Extras:
2 teasp tumeric
2 teasp mustard powder
2 tbsp cider vinegar
1 tbsp honey
ground pepper

Soak the mustard seeds in water 12-24 hours.  If there is significant water not absorbed, strain out seeds and reserve the water.  A funky smell is ok.  Put all ingredients in a blender and puree to the texture you like.   You may need to add more water to get the blender to work, but the mustard will thicken after it is made.  Pour in jars and leave at room temperature for several days to mellow before refrigerating.  This nearly filled two pint jars.

Notes:

• I bought my mustard seeds from Penzeys.
• My food processor would not grind the seeds even after almost 24 hours of soaking--they just whirled around.
• I filled one jar with the plain mixture and then blended in added half the amount given of extras to make a second jar.
• A purist would say either use vinegar or whey, not both.  But I added whey from kefir because that seemed to me extra insurance that my mustard wouldn't go bad--I gave good bacteria a head start.
• I added vinegar at the beginning of grinding the seeds because I didn't want a hot mustard.  For a hotter mustard, grind the seeds with water and let sit 10 minutes to an hour before adding whey (or vinegar, but vinegar will reduce the hotness more).  The whey will start a process of lactofermentation that will build up an effect similar to vinegar over several days.  (Traditional pickles are fermented, not made with vinegar).
• One of the frustrating things about making mustard is that you can't really taste for seasonings--it isn't going to taste good until it has sat for at least a couple of hours.