What Makes It Great: Pure hearty goodness: the richness of beefy short ribs napped in Dijon-spiked cheese sauce. You can find thinly cut boneless short ribs in many supermarkets, but especially in Asian markets, where this succulent meat is a popular choice for Korean barbecue and the Japanese dish sukiyaki. If you can't find presliced meat, freeze the short ribs for 30 minutes to firm them up; you'll get thinner slices.
12 ounces lean boneless beef short ribs, trimmed and very thinly sliced
1/4 teaspoon freshly ground black pepper
How to Make It
Preheat broiler to high.
Cut bread in half lengthwise and again crosswise. Hollow out tops and bottoms of bread, leaving a 1/2-inch-thick shell. Place bread halves on a baking sheet, cut sides up. Broil 1 1/2 minutes or until toasted.
Combine milk, flour, and mustard in a medium microwave-safe bowl, stirring with a whisk. Microwave at HIGH 1 1/2 minutes or until thickened, stirring every 30 seconds. Remove from microwave; add 1/8 teaspoon salt and cheese, stirring until cheese melts.
Heat a large cast-iron skillet over medium-high heat. Add 1 teaspoon oil to pan; swirl to coat. Add onion, garlic, bell pepper, and 1/8 teaspoon salt; sauté 5 minutes or until tender. Remove onion mixture from pan; keep warm. Add remaining 1 teaspoon oil to pan; swirl to coat. Add beef, remaining 1/8 teaspoon salt, and black pepper to pan; sauté 3 minutes or until tender.
Divide beef mixture evenly among bottom halves of bread; top with onion mixture. Drizzle cheese sauce evenly over sandwiches. Top with top halves of bread; cut each sandwich in half.