I've never heard of it before but found this link to Peter Christian's Tavern where they make and sell it:
http://www.peterchristianstavern.com/There might even be a cook book with the recipe in it that you could buy.
Here's a recipe I found that's supposedly based on the Peter Christian recipe... can't vouch for it but it might be worth a try. I found it here:
https://community.tasteofhome.com/forums/p/113333/113333.aspxHere is the mustard recipe. If you make it, let me know if you like it. It is based on the mustard they served at Peter Christian's Restaurant in Hanover, NH.
PC's Mustard
1/3 cup Coleman's Superfine dry mustard (if you use regular dry mustard the flavor is much sharper, so I prefer the Coleman's)
3/4 to 1 cup brown sugar
1/2 cup red wine vinegar (I have also used 1/4 cup white vinegar and 1/4 cup Balsamic vinegar instead and we prefer it that way)
1/4 cup water
2 beaten eggs
Mix all ingredients but the eggs in the top of a double boiler. Put the top pan over boiling water. Add eggs, one at a time, mixing well after each addition (I like to use a whisk). Cook for about half an hour or so, mixing with whisk every 5 to 10 minutes. Mustard is done when it is slightly thickened and has obviously cooked down a bit. Store in a tightly cover jar. I sterilize the jar with boiling water. Refrigerate. Serve as a dipping sauce for vegetables or pretzels or use on sandwiches.