It's worth the time
Dashi is a Japanese soup stock. This vegan version of dashi made from shiitake mushrooms and kombu seaweed will give you a gentle, mild umami flavor packed with a significant amount of natural vitamin D.
I'll be upfront in saying the way I did this recipe for homemade vegan dashi is for those who want to go the extra mile to get additional natural vitamin D...which in my opinion is worth taking the time.
This recipe will take about 2 days which indeed sounds like a lot of time but it will make total sense, and again will be worth it. This recipe is also optimally done when you have access to maximum direct sunlight exposure like in Spring and Summer.
For quick to make dashi
If you want to make vegan dashi fast, here is a great recipe for "Vegan Shiitake and Kombu Awase Dashi," by Sudachi Recipes that takes 40 minutes to make.
A cool fact about vitamin D and mushrooms
When mushrooms are exposed to direct sunlight with the gills up, they will behave like solar panels and create high levels of vitamin D2 from the sun.
From this Cooking Light article, "No One Gets Enough of This Depression-Fighting Vitamin, but a Crazy Mushroom Technique Could Change That,"
"Paul Stamets, a mycologist, author, and founder of Fungi Perfecti, notes a study he conducted during the summer in Washington state.
He found that shiitake mushrooms dried outdoors in 6 hours of sunlight over two days had more vitamin D when they were dried with their gills facing up—they went from 100 IU per 3.5 oz to nearly 46,000 IU!"
That's some serious next level vitamin D creation!
This is why I think it's worth the 2 days to get fresh shiitake mushrooms and dry them yourself in the sunlight to get that enormous amount of natural vitamin D in your mushrooms.
And the good news is that you can dry extra amounts of shiitake mushrooms while making the amount needed for this dashi recipe, and then store your newly dried vitamin D packed shiitakes and use later when you want.
From the Walmart website, here's an example of what 3.5 oz of fresh shiitake mushrooms looks like.
For maximum sunlight exposure, slice the mushrooms in pieces which will provide more surface area for exposure to sunlight.
I bought fresh whole shiitake mushrooms at an Asian market, and then sliced them up either in half or in thirds depending on how large the mushroom was.