Korean Beef Stir-Fry

Ingredients

• 3 tablespoons mirin
• 1 1/2 teaspoons chopped fresh ginger
• 2 tablespoons reduced-sodium soy sauce
• 4 cups mung bean sprouts
• 2 teaspoons cornstarch
• 1 6-ounce bag baby spinach
• 1 tablespoon canola oil
• 1/4 cup chopped fresh cilantro
• 8 ounces flank steak, trimmed of fat and very thinly sliced against the grain
• 1 teaspoon toasted sesame oil
• 1 tablespoon chopped garlic
• 2 tablespoons toasted sesame seeds, optional
• 2 teaspoons chopped jalapeno pepper, or to taste