Combine the kombu and the water in a pot and leave the kombu to soften for 30 minutes.
Once soft, place the pot on the stove and heat it up gently. You want it to just about reach boiling point without it actually getting to a proper boil. When you reach that point, fish out the kombu and discard (or better yet, use it as compost).
Now bring the liquid to a proper boil and add the smoked paprika and the nutritional yeast. Boil for about a minute before removing from heat. Your dashi stock is now done. If you are proceeding to make miso soup you can simply keep the stock simmering and continue as described below. If you are going to use the dashi stock for some other purpose, like maybe in my Japanese Spinach, you can keep it in the fridge for a few days or else freeze it in desired portions sizes.
To make the miso soup: Shortly before serving, whisk in the miso paste. Make sure there are no more lumps before adding whatever other ingredients you'd like to add, if any, and serve immediately.
You can keep miso soup in the fridge for a few days, in a sealed container.