Add the lentils to a large bowl and cover with water by several inches. Allow to soak while you caramelize the onions.
In a large pot, melt ¼ cup butter over medium heat. Add the sliced onions, cover and allow to cook for 15 minutes. Remove lid and add 1 teaspoon of salt. Cook, uncovered, on medium-low heat for 30 minutes, until onions are softened and golden brown. Be sure to stir the onions intermittently as they cook.
Meanwhile, prepare the topping by combining the cashews with 1 cup water, 1 tablespoon lemon juice, 1 tablespoon nutritional yeast, 2 tablespoons tapioca starch, and ½ teaspoon salt in a high-speed blender. Blend until smooth.
Add to a small saucepan and warm over medium-low heat. Whisk continuously, until the sauce starts to thicken and become stretchy. Remove from heat and set aside.
To the pot with the onions, add the minced garlic. Pour in the sherry vinegar. Stir to combine. Continue to cook until vinegar has reduced, for about 15 minutes.
Next, add the vegan Worcestershire, 2 bay leaves and 3-4 sprigs fresh thyme. Pour in 4 cups vegetable broth. Add the soaked and drained lentils to the pot. Cook until lentils are tender, about 20-30 minutes. Add additional cup of broth, if a more brothy consistency is desired.
Once lentils are tender, remove bay leaves and thyme stems from the pot. Ladle the soup into four separate bowls then top with a slice of sourdough bread. Cover with ¼ of the cashew cheese. Broil at 400 for 3-5 minutes, until light golden brown on top. Garnish with fresh thyme, serve and enjoy!