On a sheet pan, toss together tomatoes, onion, ¼ cup shio koji, olive oil, and black pepper. Add garlic and drizzle with more olive oil over the cut surface. Bake for 40 minutes. Remove from the oven and let cool.
Transfer the mixture into a blender along with 2 Tablespoons of shio koji, basil and water. Blend until smooth. Taste and add more shio koji to taste. Add more water if necessary for your desired consistency.
Transfer the soup to a pot and cook until warm. Scoop into serving bowls and top with milk or cream, olive oil, basil, and black pepper.
Notes
Please note that the nutritional information provided is just an estimate and accuracy is not guaranteed.