Heat olive oil in a large saucepan over medium-high heat. Add onion; sauté 2 minutes. Stir in garlic and pepper; sauté 2 minutes or until onion is tender. Add rosemary; sauté 30 seconds. Stir in broth and beans. Bring to a boil; cover, reduce heat, and simmer 15 minutes. Remove from heat; stir in lemon juice. Let stand 5 minutes. Pour half of mixture into a blender; process until smooth. Pour pureed bean mixture into a large bowl. Repeat procedure with remaining bean mixture. Spoon 1 cup soup into each of 4 bowls, and drizzle each serving with 1/4 teaspoon truffle oil.