1. Place mushroom pieces on the tray of a dehydrator with enough room to allow for generous airflow between pieces. Dehydrate, according to manufacturer's directions, at 135 degrees for 12 hours, occasionally rotating trays from top to bottom.

2. Transfer dehydrated mushrooms to a spice grinder and grind to a fine powder.

3. Preheat oven to 350 degrees. Line a baking sheet with a nonstick baking mat; set aside.

4. Place ground mushrooms, both flours, cocoa powder, sugar, salt, and porcini powder in the jar of a blender; blend until a powder is formed, about 2 minutes. Sift mushroom mixture into a medium bowl; set aside.

5. In a medium saucepan, melt butter with walnut oil over medium heat; whisk to combine. Whisk butter mixture into mushroom mixture; spread on prepared baking sheet and transfer to oven. Bake for 5 minutes; rotate baking sheet and bake for 5 minutes more. Remove from oven and let cool completely.