- In a large skillet or Dutch oven over medium heat, add the olive oil. Then add the chopped onion and sliced fennel. Cook for 3-4 minutes until softened, stirring occasionally.
- Add the chopped rosemary, garlic, and red pepper flakes. Stir to combine, and cook for another minute until the rosemary and garlic are fragrant but not browned.
- Then, add the drained and rinsed cannellini beans, chicken broth, kosher salt, and black pepper to the pot. Stir to combine, and cook over low heat until the broth has thickened, about 10 minutes.
- Add the trimmed broccoli rabe to the pot, and cook for another 4 minutes until softened, but still bright green.
- Remove the pot from the heat, and add the fresh lemon juice, and ¾ of the grated swiss to the beans. Stir to combine until the cheese has melted into the beans.
- Serve with more grated cheese, more black pepper and red pepper flakes, and toasted crusty bread for dipping.