Prepare the broth mixture: In a small bowl, combine the dashi granules with 180ml (0.75 cup) of water and stir until dissolved. Then, add the soy sauce, mirin, sake, and sugar to the dashi mixture. Stir well until the sugar is completely dissolved. Set aside.

Prepare the onions: Peel the yellow onion and slice it thinly, about 0.5cm (0.2 inch) thick. You can separate the slices into rings or half-rings.

Cook the onions: Heat 1 tsp (5ml) of vegetable oil in a medium-sized skillet or shallow pot over medium heat. Add the sliced onions and sauté for about 3-4 minutes, stirring occasionally, until they begin to soften and become translucent. Do not brown them.

Add the broth: Pour the prepared broth mixture over the softened onions in the skillet. Bring the mixture to a gentle simmer.

Simmer the onions: Reduce the heat to low, cover the skillet, and let the onions simmer for about 8-10 minutes, or until they are very tender and have absorbed some of the broth's flavor. Stir occasionally.

Add the beef: Increase the heat slightly to medium-low. Add the thinly sliced beef to the simmering onion mixture. Spread the beef slices out so they are not clumped together. The beef will cook very quickly.

Cook the beef: Gently stir the beef into the onions and broth. Cook for only 2-3 minutes, or until the beef is just cooked through and no longer pink. Be careful not to overcook the beef, as it will become tough.

Assemble the gyudon: Ladle the warm, steamed short-grain rice into two serving bowls. Spoon the beef and onion mixture generously over the rice, making sure to include plenty of the flavorful broth.

Garnish and serve: Top each bowl with a small mound of beni shoga (pickled red ginger) and a sprinkle of shichimi togarashi, if desired. For an extra rich experience, add a poached egg, soft-boiled egg, or a raw egg yolk to the center of each bowl. Serve immediately.