Growing both yellow and brown mustard? Use both seeds in this mix. Brown mustard seeds are hotter than yellow ones.
Grind ½ cup yellow and ½ cup brown mustard seeds in a spice grinder, coffee grinder or mortar and pestle. Place ground seeds in a food processor with 1 cup olive oil, 1 cup white wine vinegar, 1 tablespoon black peppercorns and 2 teaspoons chopped French tarragon and process into a smooth paste. Spoon into sterilised jars. Leave to mature for a couple of weeks before opening or presenting as gifts.