Customize it: Use carrot instead of celery root and any other white bean (gigante, cannellini) you like.
- 1 pound dried butter beans (large lima beans), soaked overnight, drained
- 1 teaspoon kosher salt, plus more
- 1¼ cups olive oil, divided
- ¾ cup finely chopped fresh parsley
- 2 garlic cloves, finely chopped, divided
- ½ small fennel bulb, chopped
- ¼ large celery root (celeriac), peeled, cut into ½-inch pieces
- 3 cups bite-size pieces Tuscan kale
- ½ cup panko (Japanese breadcrumbs)
Place beans in a large heavy pot and add cold water to cover by 1". Bring to a boil. Reduce heat, cover pot, and simmer, occasionally skimming surface, until beans are tender enough to be easily smashed with the back of a spoon, about 1 hour. Season with salt and stir in ½ cup oil.
Meanwhile, process parsley, half of garlic, and ½ cup oil in a small food processor until smooth. Cover parsley oil; set aside. Heat 2 Tbsp. oil in a large skillet over medium-low. Add onion, fennel, celery root, celery, bay leaves, remaining garlic, and 1 tsp. salt to skillet, cover, and cook, stirring occasionally, until vegetables are very soft but haven’t taken on any color, 15–20 minutes. Remove bay leaves and mix vegetables into cooked beans.
Preheat oven to 400°. Carefully purée 3 cups bean mixture and liquid in a blender until smooth and creamy; mix back into bean mixture. Stir in kale; season with salt. Pour ragout into a 3-qt. baking dish and bake until thick and bubbling and top is browned, 30–35 minutes. Let cool 10 minutes before serving. (Ragout will thicken as it sits.)
Meanwhile, heat remaining 2 Tbsp. oil in a large skillet over medium-high. Cook panko, tossing often, until golden brown, about 3 minutes. Transfer to paper towels to drain; season with salt.
Serve ragout drizzled with parsley oil and topped with toasted panko.
Do Ahead: Ragout (without panko) can be made, but not baked, 1 day ahead. Let cool; cover and chill.