Place the cashews in a blender and cover with 1 1/2 cups water. Set aside until later in the recipe.

Heat a Dutch oven or soup pot over medium-high heat and add 2 tablespoons oil and the vegan butter. When hot, add the onions and celery and cook, stirring frequently, until softened and started to brown, about 10 minutes. Sprinkle the flour over the vegetables and mix well, creating a roux. Allow to cook for a couple minutes, stirring frequently.

Add in the water a little at a time, using a whisk to stir the mixture as you go: this will help prevent lumps in the finished soup. When mostly smooth, add in the salt, pepper, bay leaves, thyme, and potatoes. Cover and bring to a boil, then reduce the heat to low and simmer for 20 to 25 minutes, until the potatoes are very tender and almost starting to fall apart.

While the soup simmers, cook the mushrooms. Heat the remaining 2 teaspoons oil in a large nonstick skillet over medium-high heat, then add the chopped mushrooms, smoked paprika, and a pinch of salt. Cook, stirring frequently, for about 5 minutes, until the liquid from the mushrooms has evaporated and the mushrooms are starting to brown. Set aside while the soup finishes simmering.

By now, the cashews soaking in the blender will be soft enough to make into cashew cream. Blend the cashews and water on high speed until smooth and creamy.

When the potatoes are fully cooked, stir in the cooked mushrooms and cashew cream, and heat until bubbling. Stir in the lemon juice, taste, and adjust seasonings as necessary.

Serve immediately - with oyster crackers, if you like.