1 fennel bulb, thinly sliced (fronds and stalks reserved)
1 yellow onion, diced
4 garlic cloves, minced
2 cups butter beans (canned, drained and rinsed)
4 cups vegetable broth, fennel stalk broth, or water
2 tablespoons olive oil, plus more for serving
1 lemon, juiced
3 sprigs fresh thyme
1/4 teaspoon red pepper flakes
Salt and black pepper
Directions
Trim the fennel: cut off the stalks and fronds and set them aside. Halve the bulb top to bottom, cut out the core with a V-shaped notch, and slice into 1/4 inch half-moons.
Heat the olive oil in a large pot over medium heat. Add the onion and cook until softened, about 5 minutes. Add the garlic and red pepper flakes and cook 1 minute more.
Add the sliced fennel and stir to coat. Cook 8-10 minutes, stirring occasionally, until soft and starting to turn golden at the edges.
Add a small splash of water or lemon juice and scrape up any browned bits from the bottom of the pot.
Add the broth, butter beans, and thyme. Bring to a boil, then reduce the heat and simmer 20 minutes.
Remove the thyme sprigs. Stir in the lemon juice and season with salt and pepper.
For a creamier soup, crush about a quarter of the beans in the pot with the back of a spoon or a potato masher.
Serve topped with chopped fennel fronds and a drizzle of olive oil.
Notes
Fennel stalk broth: simmer the trimmed stalks (and the core) in 4-5 cups water with a bay leaf, a smashed garlic clove, and a pinch of salt for 20 minutes. Strain. Start this before the main pot.
To make it heartier, add a handful of chopped kale or spinach in the last 5 minutes.
The soup thickens overnight as the beans absorb liquid. Add a splash of broth or water when reheating.