Korean Beef Noodles

INGREDIENTS

• 10 ounces shiitake mushrooms, stems removed
• 1 clove garlic, minced
• 6 cups baby spinach (about 10 ounces)
• Kosher salt
• 5 tablespoons sesame oil
• 1 1/2 tablespoons apple cider vinegar
• 1 yellow onion, cut into 1/4-inch wedges
• 1 cup shredded carrots (from about 3 carrots)
• 1 5-to-6-ounce package cellophane noodles
• 12 ounces skirt steak, sliced 1/4 inch thick against the grain
• 1/3 cup soy sauce
• 1/3 cup brown sugar