Bring a large pot of salted water to a boil. Cook the pasta until al dente. Reserve ¼ cup of the pasta cooking water and set aside. Drain and set aside.

Heat the oil in a large pot over medium heat. Add the onion and leeks and cook until softened, about 8 minutes. Melt 2 tablespoons of butter into the onion and leeks and continue cooking 5 minutes.

Remove the onion and leeks from the pot.

Melt the remaining 1 tablespoon butter into the pot and turn the heat to medium. Add the broccoli and season all over with salt and pepper. Add a big pinch of crushed red pepper. Cook for 5 minutes until bright green.

In a bowl, combine the parmesan cheese, black pepper, and fresh minced parsley and mix to combine.

Return the leeks and onion to the pot and stir to combine. Pour in the water and bring to a boil. Whisk in the parmesan-parsley mixture and stir until completely incorporated. Stir in the heavy cream and bring to a low boil. Reduce heat and simmer until just thickened.

Pour in the cooked pasta and toss to coat, adding pasta cooking water as needed. Stir in the lemon juice and toss to combine. Taste and season to your preferences. Turn off the heat.

Divide the cooked pasta between bowls and garnish with a pinch more of fresh parsley and parmesan. Enjoy!