1 cup fresh horseradish, grated (about one 6-inch root, scraped)
1 cup cider vinegar
Directions
In a glass container, combine the flour, mustard powder, salt and sugar. Stir in the horseradish and cider vinegar. Store the mustard in the refrigerator in an airtight container for 2 to 3 weeks before using. The mustard will keep for up to one month.