Feel free to use your own choice of soup ingredients, such as onions, carrots, or celery. Even apple tastes good. Simmer the soup until the vegetables have become tender.
Put the soup in a blender and blend until creamy. If you don't have a blender, you can substitute with vegetable or apple juice.
Combine the vegetable soup, sauce, soy sauce, and ketchup in a pan and bring to a boil whilst stirring.
Continue to simmer and add the sugar to taste until you reach your desired flavour. Once you have a perfect flavour, turn off the heat.
Add the flour mixed with water into the saucepan through a strainer to get rid of any lumps, mix well, then bring the mixture to a boil once again to finish.
Once cooled, pour into an empty sauce bottle and store in the refrigerator. You can make 2 bottles-full with the amounts used in this recipe.
Story Behind this Recipe
Since I want to be able eat okonomiyaki and takoyaki whenever I want, I make this sauce each time.
Even if you don't have any vegetable soup or vegetable juice, you can still make this recipe. Whenever I make stew, before I add the flavourings, I put aside some soup for okonomiyaki sauce. Since vegetable soup is quite sweet, you can reduce the amount of sugar in this recipe.