On medium high heat, melt the butter with some olive oil. Add the diced onion and 1 teaspoon of salt, sautéing for 5 minutes until the onion turns soft and translucent.

Pour in the heavy cream and let it cook, stirring frequently, until it thickens, about 5 minutes.

In a small bowl, whisk the flour with 3 tablespoon of water until smooth. Stir the flour mixture into the sauce and cook for another 5 minutes until the sauce thickens further.

Stir in the grated Parmesan cheese, ground nutmeg, and fresh spinach. Simmer until the spinach wilts, about 3-5 minutes.

Add the cooked rigatoni to the skillet and toss to coat the pasta evenly in the creamy spinach sauce.

Serve & Enjoy!