In a heavy bottom saucepan, over medium heat add the oil, garlic, shallot, and ginger
Cook stirring frequently for about 2 minutes until the shallot is translucent
Add the vinegar, brown sugar, thyme, and blueberries
reduce heat and simmer for 30 minutes, stirring and smashing the blueberries often
Pour into a fine-mesh strainer set over a bowl
Using the back of a spoon, press the mixture thru the strainer to extract all the liquid
let come to room temperature
Add the horseradish, salt and pepper, and lemon juice
With a spice grinder or mortar and pestle grind the dried celery flakes
Add the sauce and let chill in the fridge until ready to serve