1/2 cup Coleman's Dry Mustard.
1/2 cup apple cider vinegar

Mix the above and let sit overnight, then add:

1 beaten egg
1/3 cup sugar

Cook the mixture (over stove) until thick, then add:

1 cup salad dressing or mayonaise (more or less)

Wow! I love mustard, I think I am going to try this.
What does it go with? I think it should complement the taste of fried fish.

Yes it goes very well with fish fingers, grilled fish fillets.
Hope you enjoy this! and.... Same pinch, I am a mustard fan too!

I like mustard too especially like already said with fish and also with fries.
My favorite is fish n chips with mayo and mustard. But 1 don't make mustard sauce at home.