Sauté the garlic in a deep pan until golden brown. Add the soya sauce, the vegetable stock, the maple syrup, and the shiitake mushrooms and reduce the liquid until half of it has evaporated.

Rinse the seaweed in water and then soak in fresh water for 5 minutes. Add the seaweed, the miso paste, and the onion powder to the sauce. Let it simmer for 5 minutes, then pass through a fine sieve. Serve immediately or allow to cool, before decanting into a bottle. Store the vegan fish sauce in the fridge.