Cut the onions in half lengthwise, from top to bottom (axis to axis). Cut each half into ¼-inch slices, also cutting lengthwise.

Combine the soy sauce, sake, mirin, and dashi in a bowl, and set aside.

Heat the sesame oil in a large skillet over high heat. Add the beef and cook, stirring frequently, for about 2 minutes, until the beef browns slightly.

Add the sugar, and wait 10 seconds. Add the onion and cook, stirring constantly, for about 1 minute, until the onions begin to soften.

Pour the liquid mixture into the skillet. Simmer for about 5 minutes, until the ingredients cook through.

Use a large spoon to skim off any scum and fat that appear on the surface.

While the ingredients are simmering, divide the rice among 4 large bowls.

As soon as the gyudon is ready, spoon it over the rice, and serve immediately. Season with shichimi togarashi to taste and beni shoga