Instructions

1. Warm a large, heavy pot over medium heat. Add the butter and olive oil. When the butter foams, stir in the onion and cook until translucent and soft, 3 to 4 minutes. Add the garlic and red pepper flakes and cook until fragrant, about 30 seconds.
2. Add the pasta, broth, milk, salt, and black pepper. Stir well so the pasta is submerged and not clumped together.
3. Bring to a steady simmer over medium-high heat, then reduce to maintain a gentle simmer. Cook uncovered, stirring frequently, until the pasta is al dente and the liquid has reduced to a saucy consistency, 9 to 11 minutes.
4. Lower the heat to low and pour in the heavy cream. Simmer for 1 minute, stirring, to warm and combine.
5. Remove the pot from the heat. Add the Parmesan a handful at a time, stirring vigorously after each addition until fully melted and glossy.
6. Stir in the cream cheese cubes until they melt and the sauce turns silky and smooth.
7. Add the lemon zest and lemon juice. Taste and adjust seasoning with additional salt and pepper if needed.
8. Fold in the spinach and peas. Cover the pot and let sit for 1 minute to wilt the greens and heat the peas through.
9. If the sauce is thicker than you like, stir in a splash of hot water or warm milk to loosen. Let the pasta rest 2 minutes so the sauce clings, then sprinkle with parsley and serve immediately.