Make sweet potatoes: Peel sweet potatoes. Slice lengthwise, then cut into 1-inch pieces. Place in a medium saucepan and cover by 1-inch with salted water. Cover and bring to a boil. Simmer sweet potatoes, uncovered, until potatoes are tender, about 13 minutes. Drain, then return to saucepan. Cover to keep warm.

Prep vinaigrette: Halve shallot, then peel and finely chop. In a liquid measuring cup, whisk together 1⁄2 cup water, beef broth concentrate, and mustard.

Marinate shallots: In a medium bowl, whisk together 2 tablespoons oil, 1 tablespoon vinegar, and a pinch each salt and pepper. Stir 2 tablespoons shallots into

vinaigrette (save rest for step 5) and set aside to marinate.

Cook pork tenderloin: Pat pork dry. Slice, crosswise, into 1⁄2-inch thick medallions (about 6). Season all over with 1⁄2 teaspoon salt and several grinds of pepper. Heat 1 tablespoon oil in a medium skillet over medium-high. Add pork and cook until well browned and slightly pink in the center, 2–3 minutes per side. Transfer to a plate and cover to keep warm.

Make sauce: Add remaining shallots and 1 teaspoon oil to skillet and cook until shallots are softened and browned, about 1 minute. Stir broth mixture, then add to skillet. Bring to a simmer, then cook until thickened and reduced to about 1⁄4 cup, 3–4 minutes. Remove from heat and stir in half of the sour cream. Season to taste with salt and pepper.

Finish & serve: Return sweet potatoes to medium heat. Add remaining sour cream and 2 tablespoons oil, then mash with a fork or potato masher until creamy. Season to taste with salt and pepper. Toss arugula with vinaigrette. Serve pork, with sauce spooned over top, alongside salad and mashed sweet potatoes.