What is a Prepared Mustard Substitute? When a recipe calls for prepared mustard, use 1 teaspoon dry mustard (ground mustard) for 1 tablespoon prepared mustard, and add the same amount of water or vinegar to make up for the missing liquid.

For each teaspoon of ground mustard, include 2 teaspoons of liquid. If you use just water, your mustard will most likely be bitter. Try using a teaspoon of water and 1 teaspoon of vinegar.

Brands of dry mustard powder, including McCormick and Colman's, recommend mixing the powder with water and allowing it to sit for 10 minutes to develop the fullest sharp, tangy flavor.

The pungent flavour of mustard diminishes very quickly when it is heated. If it's a warm sauce the problem will solve itself. If it's cold, you can try to dilute it with yoghurt or sour cream or add a neutral vegetable like cucumber or potato. Mustard brings spice, salt and acid.