Try this recipe with your favorite herb seasoning blend in place of County Clare and add salt to taste if necessary.
Stir mustard seeds, vinegar and beer together, then cover with plastic wrap and let stand overnight. Blend in a food processor to desired consistency. Save remaining beer you opened for the original ingredients so you can add additional beer 1 Tbsp. at a time if your mustard is too thick. Stir in seasoning, transfer to a sealable, glass container and refrigerate for 2 to 4 days before using.