How to Make It
In a small saucepan, boil the apple cider over high heat until reduced to 2 tablespoons, about 10 minutes; let cool.
In a large bowl, combine the reduced apple cider with the vinegar and shallot. Whisk in the mustard and oil and season with salt and pepper. Add the baby greens and toss. Divide the salad among 10 plates and serve.