Heat 1 tsp. oil in large skillet over medium heat. Add leek and sauté 2 minutes. Stir in beans, broth, garlic, and thyme. Cover, reduce heat to low, and simmer 8 minutes. Season with salt and pepper. Transfer bean mixture to food processor, and blend until creamy and smooth. Return to skillet, cover, and keep warm.Heat remaining 1 tsp. oil in medium skillet over high heat. Add mushrooms and sauté 8 minutes, or until soft and brown. Season with salt and pepper, and stir in parsley.Spoon whipped bean mixture into shallow bowls. Top with equal portions of mushrooms. Drizzle each serving with 1/2 tsp. truffle oil, and serve.