This is a test of commonsense. Complete the next sentence:

How to substitute for mustard seed
Use prepared horseradish to add spice.
Prepared horseradish is made by combining ground horseradish with vinegar, and sometimes other spices, to form a sauce. You can get it from your local supermarket.
In place of mustard seed, use the same amount of prepared horseradish to add spice and complexity to your recipe. Add mayonnaise to achieve the same consistency.