Soak the cashews overnight or bring a large pot of water to a boil, pour over the cashews in a bowl and let sit for 3 hours. Drain and rinse the cashews.
To make the shiitake powder: Grind 3 dried shiitake mushrooms in a small grinder or food processor until you get a very fine powder. Set aside 1/2 tsp powder and keep the leftover in a airtight container for other uses.
Add the cashews to the bowl of a blender with the water, white miso, cognac, nutritional yeast, tahini, shiitake powder and truffle oil.
Melt the cocoa butter in a small saucepan and mesure 1/4 cup of melted cocoa butter, add them to the blender. Do the same for the coconut oil.
Add the salt and pepper and blend until completely smooth, scraping down the sides from time to time. The mixture will be very thick, if you don't have a powerful blender, use a food processor.
Stack two 3-inch (2.75-inch tall) cake rind molds and line with parchment paper (sides and bottom). Pour the mixture into the molds and flatten the top. Alternatively, you can use any pan you have on hand: round, rectangular, etc. Smooth the top using a knife and cover with plastic film.
Place in the refrigerator for at least one day, it will become a lot more firmer and the flavors will have time to merge.
For the yellow fat (optional): Melt the refined coconut oil and turmeric over low heat and mix well. Let sit at room temperature until the coconut oil becomes spreadable again. Using your fingers, spread some colored coconut oil around the foie gras to make it look like yellow fat.
Serve cold and spread on toasted bread, crackers, etc. This vegan foie gras pairs well with sweet white wines.