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 canner, jars & lids.
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).
Fill hot jars to a generous 1/4-inch headspace (more like 1/2-inch), tamping down the mustard into the jar. Thoroughly bubble by passing the handle of a wooden spoon along the edges and middle of the jar. Wipe rims, affix lids and process in a boiling water bath for 10 minutes. Allow to rest for 5 minutes in the hot water prior to removing from the canner.