Combine bourbon, water and mustard seed in a small bowl. Mix to wet all seeds, and then allow to steep until nearly all of the liquid is absorbed, about 4 hours, or overnight. Alternatively, heat bourbon, water and seeds until mixture just comes to a boil; remove from heat and steep for about 2 hours.
Prepare a boiling water bath canner and enough jars to hold 3 cups of product.
Transfer soaked seeds to the bowl of a food processor; process until smooth, or leave grainy, as you prefer (my mini Cuisinart will not get the mustard entirely smooth). Add vinegar, mustard powder, sugar, and salt and process briefly to mix. Transfer to a medium saucepan.
Over medium heat, stirring constantly, bring mustard to a boil; continue to boil mustard until it reduces to your desired thickness, remembering that it will thicken further upon cooling (I cooked mine for about 3 minutes). Taste and adjust seasonings (add additional water if you need to tinker with the flavor and the mustard is getting too thick).
Funnel the finished mustard into the prepared jars, leaving a generous ¼-inch headspace (more like ⅓-inch). Remove air bubbles with a bubbling tool or chopstick (wood or plastic only). Wipe the rims, apply the lids and rings, and process in a boiling water bath canner for 10 minutes.
When the time is up, remove the lid from the pot and turn off the heat. Let the jars rest in the cooling water for five minutes. When that time is up, remove jars and set them on a folded kitchen towel to cool. When the jars have cooled enough that you can comfortably handle them, check the seals. Sealed jars can be stored at room temperature for up to a year. Any unsealed jars should be refrigerated and used promptly.