1. Bring 4 quarts water to boil in a large pot.

2. Fill large bowl halfway with ice and water.

3. Add broccoli rabe and 1 tbsp salt to boiling water and cook until crisp-tender, about 1 minute.

4. Using slotted spoon, transfer broccoli rabe to ice water and let cool, about 2 minutes; drain and pat dry.

5. Return pot of water to boil, add pasta, and cook, stirring often, until just starting to soften, about 5 minutes.

6. Drain pasta in colander and toss with 1 tbsp olive oil. Leave in colander and set aside.

7. Preheat oven to 400 F.

8. Dry pot and heat 1 tbsp oil over medium heat.

9. Add sausage and cook, breaking up meat with spoon, until no longer pink, about 3 minutes.

10. Using a slotted spoon, transfer sausage to paper towel-lined plate.

11. Pour off all but 1 tbsp fat from pot, add onion and 1/2 tsp salt, and took until softened and lightly browned, 5-7 minutes.

12. Stir in garlic, anchovies, lemon zest, and pepper flakes and cook until fragrant, about 30 seconds.

13. Add flour and cook, stirring constantly, until golden, about 1 minute.

14. Slowly whisk in broth, cream, and wine, scraping up any browned bits and smoothing out any lumps.

15. Bring to simmer and cook until thickened slightly, about 2 minutes.

16. Off heat, gradually whisk 1 cup fontina and 1/2 cup Parmesan into sauce until cheese is melted and sauce is smooth.

17. Stir in lemon juice, broccoli rabe, pasta, and sausage, breaking up any clumps.

18. Season with salt and pepper to taste.

19. Transfer to 13x9 baking dish and sprinkle with remaining 1 cup fontina and 1/2 cup Parmesan.

20. Place baking dish on aluminum foil-lined baking sheet and bake until golden and bubbling around the edges, 25-35 minutes.

21. Allow to cool 20 minute before serving.