Preheat the oven to 450°F with a rack in the center position
Place a rimmed baking sheet in the oven while it preheats
Bring a large pot of salted water to a boil over high heat
Add the pasta and cook until al dente according to package instructions
Reserve ¼ cup pasta water and drain.Meanwhile, add the fennel, 2 tablespoons of olive oil and ½ teaspoon of the salt to a large bowl and toss to coat
Once the oven is preheated, carefully remove the baking sheet
Add the fennel to the sheet in a single layer
Return the sheet to the oven and roast until browned, about 10-12 minutes
In a large skillet, heat the remaining 1 tablespoon olive oil over medium heat
Once the oil is glistening, add the shallots, and cook until softened, about 5 minutes
Add the garlic and fennel seeds and cook, stirring, until fragrant, 1-2 minutes
Stir in the white wine and cook until reduced by half, about 4 minutes more
Stir in the cream and bring to a simmer
Add the lemon zest, remaining ¼ teaspoon salt, and pepper and stir to combine
Stir in the reserved pasta water and reduce the heat to medium low
Simmer until slightly thickened, about 6 minutes.Add the pasta, roasted fennel, lemon juice, and pepper flakes, if using, to the pan and toss until well combined
Divide the pasta between 4 plates and garnish with the fennel fronds
Sprinkle with pepper and Parmesan if using