01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - Slice the leeks lengthwise, wash thoroughly, then cut into 1-inch pieces. Place leeks, garlic cloves, carrots, and celery on the prepared baking sheet. Drizzle with 2 tbsp olive oil, sprinkle with salt and pepper, and toss to coat.
03 - Roast vegetables in the preheated oven for 25–30 minutes, stirring once, until leeks are golden and vegetables are tender.
04 - In a large pot, heat remaining 1 tbsp olive oil over medium heat. Add roasted vegetables, cannellini beans, thyme, and bay leaf. Pour in vegetable broth. Bring to a simmer and cook for 10–15 minutes, allowing flavors to meld.
05 - Remove the bay leaf. Use an immersion blender to puree the soup until creamy but still slightly chunky, or blend in batches in a countertop blender (vent lid to avoid steam buildup).
06 - Stir in heavy cream. Taste and adjust salt and pepper as needed.
07 - Ladle soup into bowls. Garnish with fresh parsley and serve with crusty bread if desired.