Preheat your oven to 425°F (220°C). Toss the cauliflower florets with 1 tablespoon olive oil, 1/2 teaspoon salt, and 1/2 teaspoon black pepper. Spread them in a single layer on a baking sheet. Roast for 25-30 minutes, tossing halfway through, until the cauliflower is golden brown and tender.
While the cauliflower roasts, bring a large pot of salted water to a boil. Add the 12 oz farfalle pasta and cook according to package instructions until al dente, about 11 minutes. Reserve 1 cup of the pasta cooking water before draining.
In a large skillet, heat the remaining 1 tablespoon of olive oil over medium heat. Add the chopped leeks and cook, stirring occasionally, until they soften and become translucent, about 5-7 minutes. Add the minced garlic and cook for another 1-2 minutes until fragrant.
Reduce the heat to low and pour in the 1 cup heavy cream. Stir in the grated Parmesan cheese, nutmeg, and the remaining salt and black pepper. Allow the sauce to simmer gently for 3-5 minutes, stirring frequently until it thickens slightly. Add reserved pasta water as needed to adjust consistency.
Add the roasted cauliflower to the skillet with the creamy leek sauce. Toss gently to coat. Then add the cooked farfalle pasta and fold everything together carefully, ensuring even coating and distribution.
Remove from heat, sprinkle the chopped fresh parsley over the pasta, and give it one last gentle toss. Serve immediately with extra Parmesan cheese if desired.
