Combine 8 cups water with 1 piece kombu, 2 dried shiitake mushrooms, and 1 onion half
Let sit for 30 minutes
Heat slowly until just below a boil
Remove kombu before boiling
Simmer 20 to 30 minutes
Add 2 to 3 slices ginger and 2 smashed garlic cloves
Add 2 to 3 green onion tops
Simmer 20 to 30 more minutes
Strain the broth
Season with salt, soy sauce, and a little mirin to taste
Use immediately for ramen or keep warm until serving