Heat a medium sized pot over medium. Once hot, add the oil.
Sauté the onion for 2-3 minutes until translucent.
Add the mushrooms and allow to cook until lightly brown. Add the sake and leave to evaporate over medium heat.
Pour the vegan dashi or stock into the pot.
For the curry cubes, I like to chop these into smaller pieces to dissolve easily.
Place the cubes in a small strainer or laddle with holes. Submerge into the soup and mix to dissolve.
Season the curry with salt, sugar and soy sauce, to taste, if desired.
Leave the curry to simmer over medium low heat until it starts to thicken.
For the udon, I used frozen sanuki udon and simply microwaved the noodles for around 2 minutes in a bowl with a lid until chewy. You can also boil the udon until chewy and separated.
Once the curry has thickened, you can add more dashi or stock to run it down, if desired. I personally prefer a thicker soup base to coat the noodles.
Pour the soup over the noodles. Top with green onions. Finish with some chili oil or powder for extra heat, if you'd like. Enjoy while hot!