1In large saucepan or Dutch oven, heat oil over medium heat. Add leeks, garlic and shallot. Cook 5 minutes, stirring occasionally, until leeks and shallot are softened but not browned. Add cauliflower, broth and herbes de Provence. Cover; cook until cauliflower is tender, about 20 minutes.
2Meanwhile, in 10-inch skillet, cook bacon until crisp. Drain on paper towels; set aside.
3Remove soup from heat; using blender or handheld immersion blender, puree soup until smooth. If using regular blender, return soup to saucepan. If using immersion blender, return saucepan to heat. Add salt, pepper and butter. Cook over low heat 5 minutes, stirring occasionally, until butter is melted and soup is hot.
4To serve, ladle soup into bowls. Sprinkle with bacon.