Combine the blueberries, water, sugar and lemon zest in a medium saucepan and bring to a boil over medium-high heat.
Reduce the heat to medium-low and allow to simmer until reduced by about half, stopping to smash the berries every now and again, about 15-20 minutes. Until the sauce is reduced and has thickened slightly.
Remove from heat and set aside.
Meanwhile, in another saucepan or in a medium pot, melt butter over medium-high heat. Add onion and garlic and saute until softened and translucent, about 3-5 minutes.
Sprinkle in thyme, vinegar, hot sauce, and blueberry mixture and bring to a bubble, then reduce to a simmer and allow to cook for another 6-8 minutes until the mixture has thickened a bit. Remove from heat and cool slightly.
Pour the mixture into a blender or food processor and blend to desired consistency, or leave chunky if desired. (Be careful blending hot liquids.)
Pour into a jar with a tight fitting lid and refrigerate until ready to use.