Begin by cutting the beef chuck roast into 1.5-inch cubes, ensuring they are uniform for consistent cooking. Pat the beef cubes dry with paper towels and season generously with salt and pepper.

In a large Dutch oven, heat 2 tablespoons of vegetable oil over medium-high heat. Sear each side of the beef cubes for about 3-4 minutes until browned. Transfer to a plate and set aside.

In the same pot, lower heat to medium and sauté chopped onion for 4-5 minutes until translucent. Add minced garlic and grated ginger, cooking until fragrant, about 1 minute.

Return the seared beef to the pot. Pour in the soy sauce, beef broth, brown sugar, and rice vinegar. Add red pepper flakes if desired, and stir gently.

Bring to a simmer, cover, and reduce heat to low. Let braise for 2-3 hours, stirring occasionally until beef is fork-tender.

Create a cornstarch slurry by mixing cornstarch with cold water. Slowly drizzle into the pot, stirring until sauce thickens, about 2-3 minutes.

Serve hot over rice or noodles, or in lettuce wraps, garnished with cilantro or sesame seeds.