Beef Udon Soup (Niku Udon)

In a medium pot, bring 4 cups of water to a gentle simmer. Stir in the instant dashi powder until dissolved, then keep the broth warm over low heat. Bring a second pot of water to a boil for the udon noodles.

Heat the neutral oil in a large skillet over medium-high heat. Add the sliced onion and cook for 7 to 8 minutes, stirring often, until softened and lightly golden. Add the thinly sliced beef and sugar, then cook for 2 to 3 minutes until the beef is just browned.

Pour 1/2 cup of the warm dashi into the skillet, then add 1 tbsp mirin, 1/2 tbsp soy sauce, and the oyster sauce. Bring to a simmer and cook for about 10 minutes, until the onions are tender and the liquid reduces to a light savory sauce.

Season the remaining dashi broth with the remaining 1 tbsp mirin and 1/2 tbsp soy sauce. Taste and adjust if needed. Cook the udon noodles in the boiling water according to the package directions, then drain well.

Divide the cooked udon between 2 serving bowls. Ladle the hot broth over the noodles, then top with the beef and onion mixture. Finish with sliced scallions and serve immediately.