Q. Is there a substitution for dry mustard?
How about prepared mustard? Dry mustard packs more of a punch, so use two to three times as much prepared mustard in making the substitution. Also, if the amount of moisture is critical to the recipe you're using, decrease the amount of water or other liquid in the recipe to compensate for the water and vinegar in the prepared mustard.
The general rule for substitution is to use a tablespoon of prepared mustard for each teaspoon of dried mustard and vice versa. If you're substituting dried mustard for prepared mustard and need the additional moisture in your dish, add a teaspoon of water for each teaspoon of dried mustard.