In a cup, stir the dry mustard into the hot water until dissolved. Let sit for 5 minutes. Combine the mustard mixture and all the remaining ingredients in a saucepan. Bring to a simmer over low heat and simmer, stirring frequently, until all the fruits are soft and the mixture has thickened, about 30 minutes. Remove from the heat and let cool. Place in a blender or food processor and puree until smooth. This mustard will keep for weeks in the refrigerator.
