How to Make It
In a small saucepan, bring the apple juice to a boil with the cinnamon stick and the lemon zest. Simmer over moderate heat until the liquid is reduced to 2 tablespoons, about 5 minutes. Discard the cinnamon stick and lemon zest and pour the liquid into a small bowl; let cool slightly. Add the cider vinegar and shallot and season with salt and pepper. Whisk in the grapeseed oil until emulsified.
In a large bowl, toss the celery root, cucumber, carrots, grapes, feta cheese, mesclun and romaine. Whisk the apple vinaigrette again and add to the salad, season with salt and pepper and toss to coat. Serve right away.