Bring 4 cups of water to a rolling boil in a large pot. Add 1 tablespoon kosher salt. Add 12 oz dried pasta and cook uncovered, stirring occasionally, until pasta is al dente according to package time (typically 8–11 minutes). Reserve 1 cup of pasta cooking water, then drain pasta and set aside.

Sauce Base

While pasta cooks, heat 2 tablespoons olive oil and 1 tablespoon butter in a large skillet over medium heat until the butter melts and foams.

Add 1/2 cup finely diced onion and sauté, stirring occasionally, until translucent and soft, about 4–5 minutes.

Add 3 minced garlic cloves and 1/4 teaspoon crushed red pepper flakes. Cook, stirring constantly, until fragrant, about 30–45 seconds — do not let garlic brown.

Tomato & Cream

Stir in 14 oz crushed tomatoes and 1 tablespoon tomato paste. Bring to a gentle simmer and cook 5–7 minutes to thicken slightly and develop flavor.

Reduce heat to low and stir in 1/2 cup heavy cream until the sauce is smooth and a uniform color. Taste and season lightly with salt and freshly ground black pepper.

Vegetables & Add-ins

Add the reserved drained pasta to the skillet with the sauce. Toss to combine over low heat.

If the sauce seems thick, add reserved pasta cooking water a few tablespoons at a time (up to 1/2 cup) until the sauce coats the pasta to your liking.

Fold in 2 cups chopped baby spinach and 1/2 cup grated Parmesan. Cook, tossing, until the spinach wilts and the cheese melts into the sauce, about 1–2 minutes.

Seasoning & Finish

Remove the skillet from heat. Stir in 1 teaspoon lemon zest and 1/4 cup torn fresh basil leaves, if using. Adjust seasoning with additional salt and freshly ground black pepper to taste.

Divide the pasta among plates or bowls and garnish with extra grated Parmesan and a drizzle of olive oil if desired. Serve immediately.