Mise en place - Trim, peel, and slice the carrots into 4-inch sticks.
Make the pickling liquid - Bring the vinegar, brown sugar, and salt to a boil. Take off the heat and allow the brine to cool a bit.
Marinate the carrots - Pour the pickling liquid over the carrot sticks, and marinate for at least three hours. Drain and stash in the fridge until ready to serve.
Garnish and serve - Mince the parsley leaves, enough to yield ¼ cup. Toss the drained carrot sticks with 1 T grapeseed oil and 1 T prepared horseradish. Sprinkle the minced parsley over the dressed carrots.