Pour 2 cups boiling hot water over cashew pieces and let sit for at least 2 hours. Drain and rinse cashew pieces. Place in high-speed blender; add ¾ cup fresh cold water. Blend for 1 minute, starting at slow speed, gradually going up to high speed, until creamy. Reserve ½ cup for the recipe, and store the rest in the fridge for another use.
For mushroom pasta
Cook the pasta in a large pot of water according to package instructions in salted water; remove 2 minutes before recommended cooking time. Reserve ½ cup of pasta water.
While pasta is cooking, heat a large skillet over medium heat for 3 minutes; add olive oil. Once shimmering, add shallots and garlic, and saute until lightly golden, for approximately 3 minutes. Reduce heat if necessary to avoid burning.
Add sauteed mushrooms, chopped sage, and ½ teaspoon sea salt. Saute for approximately 5 minutes, stirring occasionally, until edges of mushrooms are browning.
Using the pot the pasta was cooked in, add ¼ cup pasta water, ½ cup cashew cream, pasta, mushrooms, and kale. Taste and adjust seasoning to taste. Serve in shallow bowls, freshly ground black pepper, vegan Parm, and truffle carpaccio, if desired.