- 1 3-3 1/2-pound boneless pork loin
- Kosher salt, freshly ground pepper
- 1 cup whole grain mustard
- 1/4 cup mustard powder
- 1/2 cup olive oil, divided
- 2 cups farro
- 1/3 cup apple cider vinegar
- 1 tablespoon caraway seeds, coarsely chopped
- 1 teaspoon honey
- 1 1/2 pounds baby carrots, any color, very thinly sliced lengthwise on a mandoline
- 1/2 small red onion, very thinly sliced into rings
- 1 cup (packed) fresh flat-leaf parsley leaves
Place pork on a wire rack set inside a large rimmed baking sheet; season all over with salt and pepper. Whisk mustard, mustard powder, and 1/4 cup oil in a small bowl to blend. Rub over pork and let sit at room temperature 1 hour.
Preheat oven to 425°F. Roast pork until beginning to brown, 25-30 minutes. Reduce heat to 350°F and roast until a thermometer inserted in the thickest part registers 145°F, 25-35 minutes longer, depending on thickness of roast.
Meanwhile, cook farro in a large pot of boiling salted water until tender, 30-35 minutes; drain.
Whisk vinegar, caraway seeds, honey, and remaining 1/4 cup oil in a medium bowl; set vinaigrette aside.
Heat 2 tablespoons vinaigrette in a large skillet over medium-high heat. Add farro and carrots and cook, tossing often, until carrots soften and farro is warmed through, about 3 minutes. Remove from heat and transfer to a large bowl. Add onion, parsley, and half of remaining vinaigrette; season with salt and pepper and toss to combine.
Slice pork. Serve with farro salad. Pass remaining vinaigrette alongside.
DO AHEAD: Farro can be cooked 2 days ahead. Let cool, cover, and chill. Reheat before using.