Heat the vegan butter or coconut oil in a pan over medium heat. Add the leek together with the onion and cook for about 10 minutes. Stir until the onion becomes soft and add the garlic, ginger, fresh tomato and tomato paste. Cook for another few more minutes until fragrant.
Transfer the ingredients into a blender and add the miso paste, soy sauce and tahini. Blend for a minute or two until the mixture becomes a paste.
Heat in a large pot a little bit of coconut oil and add the paste. Let it simmer for a moment before you add the homemade broth or water.
Rinse the kombu and add it to the pot. Reduce heat to low and simmer.
Soak the cashew nuts in 100 ml of warm water for around 20 minutes, then blend to a smooth consistency. If you do not have cashews or do not want to make cashew nut milk, you can always use any plant based milk.
Mix in a separate bowl the sesame oil, sriracha, rice vinegar, maple syrup, soy sauce and garlic powder. This will give our ramen an extra umami kick.
Before finishing the broth remove the kombu and right before serving, add the cashew nut milk and the umami mixture.