Having a map of Westeros is really handy in this case... I was completely confusing Oldtown with Moletown and had associated this mustard with life in the North. After checking out a map, I found that this is actually a more Southern town which makes a whole lot more sense after trying the stuff.
Tossing it back over to my heroes at Inn at the Crossroads, you can find 2 different recipes for Oldtown Mustard here:
I doubled up on my first batch which filled up 4 of the medium sized jars that I have. And with no real way to grind up the nuts I ended up tossing them in a smoothie cup that attaches to my blender. That was fun! Also a very good idea to grab a 10$ coffee bean grinder to grind the mustard down if you don't have one already... this thing saved me TONS of time.... sanity... broken windows and maybe even a devastating sense of monotony as you grind these puppies by hand the old fashioned way. Yes, I wanted to keep this as period appropriate as possible but that doesn't mean I'm not going to throw a little modernism in there to make things a bit easier on me. Have you seen how much I'm doing here? Whew. Thank goodness for small electric kitchen appliances. Thank goodness.
I got the mustard made and working in the fridge out in the garage and feeling quite accomplished. After a few days to let it set, I went into the fridge to test it, popped the top off of my beautiful jar and watched helplessly as it crashed to the cold concrete garage floor... Ugh. I think a little piece of me died as it's pieces scattered across the floor like cockroaches.
Protip: You're going to want to try it and if you get jars like this, open them up over some carpet.