Bring a large pot of salted water to a rolling boil. Add the Conchigliette pasta and cook according to the package instructions until al dente.

Reserve about ½ cup of pasta water before draining. This starchy water can be used later to adjust the sauce’s consistency if necessary.

While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the diced onion and cook until softened and translucent.

Stir in the minced garlic and cook for another minute until fragrant. Be careful not to brown the garlic, as it can develop a bitter taste.

Pour the heavy cream into the skillet and stir gently to combine with the onions and garlic. Add the Italian seasoning, salt, and black pepper.

Allow the mixture to simmer for several minutes until slightly thickened. The cream should become smooth and silky while developing flavor.

Gradually stir in the grated Parmesan cheese until fully melted into the sauce.

Add the baby spinach and cook for a minute or two until wilted. The sauce should be creamy, rich, and evenly combined.

Add the drained Conchigliette pasta to the skillet and toss gently until every shell is coated in the creamy Parmesan sauce.

If the sauce becomes too thick, add a splash of the reserved pasta water until the desired consistency is reached.

Transfer the pasta to serving bowls and garnish with fresh parsley, extra Parmesan cheese, lemon zest, or red pepper flakes.

Serve immediately while warm and creamy for the best flavor and texture.