Melt 1 tablespoon butter in large skillet, medium heat.
Add cremini mushrooms, spread evenly.
Cook for about 5 min., flip. Cook additional 5 min. until tender, lightly browned.
Remove mushrooms, reserve on a plate.
Melt 2 tablespoons of butter in skillet. Add oyster mushrooms. Spread evenly.
Cook for 10 minutes, flipping two or three times until tender with brown spots.
Remove oyster mushrooms from skillet, reserve on a plate.
Melt remaining 2 tbspns of butter in skillet. Add shallot. Cook until soft, translucent - about 5 minutes. Stir occasionally. Add garlic. Cook 1 minute, until very fragrant.
Add sherry and thyme to skillet and return all mushrooms to skillet. Stir, bring liquid to a simmer. Cook for 5 minutes until most of liquid is absorbed. Remove from burner.
Cool mixture for a few minutes. Then transfer to food processor with an S blade. Add walnuts and truffle oil.
Blend mixture until it is as smooth as you prefer — coarse or very smooth. Season with salt and pepper. Serve immediately with your choice of bread or crackers or chill for later. Makes about 2 cups.