Cut the beef into bite-sized pieces. Thinly slice the onion, roughly chop the cabbage, and slice the green onion.

Heat a frying pan and add 1 tablespoon of oil. Sauté the beef and onion with salt and pepper.

When the beef is almost cooked through, add the cabbage and continue to stir-fry.

Add the udon noodles, mentsuyu, and sugar. Stir-fry, loosening the noodles as you go.

Season with soy sauce, salt, and pepper to taste. Add the green onion and quickly toss everything together.

Serve on a plate and generously top with bonito flakes.