In a large pot, bring the broth to a boil over medium-high heat.
Add the soy sauce, mirin, sugar, grated ginger, and minced garlic to the pot. Stir well to combine.
Reduce the heat to low and let the broth simmer for about 10 minutes to allow the flavors to meld together.
While the broth is simmering, cook the udon noodles according to the package instructions. Drain and set aside.
Add the sliced mushrooms, bok choy or spinach, and half of the sliced green onions to the pot. Cook for about 5 minutes until the vegetables are tender.
To serve, divide the cooked udon noodles among bowls. Ladle the hot soup over the noodles, making sure to include some of the vegetables and broth in each bowl.
Garnish with the remaining sliced green onions and any optional toppings you desire, such as sliced cooked chicken, tofu, or shrimp.
Serve the udon soup hot and enjoy!Feel free to adjust the ingredients and seasonings according to your taste preferences. Enjoy your homemade udon soup!