Step 1

Bring 2 cups water to a boil in a small saucepan over high heat. Add cashews and boil until tender, 13 to 15 minutes. Drain the cashews and transfer to a blender; add the remaining 3/4 cup water. Secure the lid on the blender and remove the center piece to allow steam to escape. Place a clean towel over opening. Process until smooth, about 45 seconds. Add nutritional yeast, vinegar, garlic powder, mushroom powder and 1/4 teaspoon salt; process until incorporated, about 15 seconds.

Step 2

Melt 1 tablespoon butter in a large skillet over medium-high heat. Add onion and cook, stirring occasionally, until softened, about 5 minutes. Add spinach in batches, folding with tongs until all the spinach fits in the pan. Cook, stirring occasionally, until completely wilted, about 3 minutes. Continue cooking, stirring occasionally, until the liquid has evaporated, about 5 minutes. Add the cashew cream mixture and the remaining 1/4 teaspoon salt and 1 tablespoon butter; reduce heat to medium and cook, stirring constantly, until heated through, about 2 minutes. Serve immediately.