Prepare udon noodles according to the package instructions. Drain and set aside.
In a medium pot or deep pan, heat a little oil over medium heat. Add the sliced onion and sauté until soft and translucent.
Add the thinly sliced beef to the pan and cook until browned and just cooked through.
Pour in 2 cups of water. Stir in the dashi powder, soy sauce, and mirin. Bring to a gentle boil.
Lower the heat to a simmer. Break the curry blocks into pieces and add them to the pot. Stir until completely dissolved. Let simmer for about 5 minutes, or until the broth thickens slightly.
Drizzle whisked eggs in the broth
Divide the cooked udon into serving bowls. Ladle the hot curry broth and beef mixture over the noodles.
Top with chopped green onions. Serve hot and enjoy!