1 large head celery root, peeled, halved, and cut into 1/4-inch wedges
3 medium carrots, thinly sliced
1 tablespoon olive oil
2 boneless rib eyes, excess fat trimmed
1 tablespoon unsalted butter, room temperature
2 teaspoons prepared horseradish
1 teaspoon Dijon mustard
1/4 cup sliced fresh chives
Heat broiler, with rack 8 inches from heat. On a rimmed baking sheet, toss celery root and carrots with oil and arrange in an even layer. Pat steaks dry and add to sheet; season vegetables with salt and pepper.
Broil until vegetables are tender and steaks are browned, 8 to 10 minutes, flipping vegetables halfway through.
Tent steaks with foil and let rest 10 minutes. Stir together butter, horseradish, and mustard; season with salt and pepper and spread on steaks. Sprinkle with chives to serve.