Bring a large pot of salted water to a rolling boil and add your pasta. Cook according to package directions until al dente (about 8-10 minutes), then drain and set aside. Reserve 1/2 cup pasta water for later—it helps create a silky sauce texture.

While the pasta cooks, heat olive oil in a large skillet over medium heat. Add your diced onion and sauté for 3-4 minutes until softened and fragrant, then add minced garlic and cook for another 30 seconds until aromatic.

Sprinkle flour over the onion mixture and stir constantly for about 1 minute to create a roux base. This thickens your creamy spinach sauce beautifully and prevents lumps from forming during the cooking process.

Pour in the vegetable broth and whole milk, stirring continuously until the mixture thickens slightly (2-3 minutes). Add the heavy cream, butter, Parmesan, salt, pepper, Italian seasoning, and nutmeg, whisking until smooth and homogeneous.

Add the fresh spinach in batches, stirring after each addition until wilted—this takes about 2-3 minutes total. The spinach reduces significantly, so don't worry about overfilling your skillet.

Stir in the fresh lemon juice and taste your cozy creamy spinach pasta recipe, adjusting seasonings as needed. Add reserved pasta water one tablespoon at a time if the sauce seems too thick.

Add the cooked pasta to the creamy sauce and toss gently until every strand is coated. Cook together for 1-2 minutes to marry the flavors, then serve immediately while hot and fragrant.