Heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the Italian sausage and cook, breaking it apart with a spoon, until browned and cooked through, about 5-7 minutes. Use a slotted spoon to transfer the sausage to a plate, leaving the drippings in the skillet.

Add the diced onion to the same skillet and sauté for 3-4 minutes until softened. Add the minced garlic and cook for another minute until fragrant.

Stir in the chopped sun-dried tomatoes, Italian seasoning, and red pepper flakes (if using). Cook for 1 minute.

Pour in the chicken broth, scraping up any browned bits from the bottom of the pan. Bring to a simmer and cook for about 3-4 minutes, allowing the sauce to reduce slightly.

Reduce the heat to low and stir in the heavy cream. Bring to a gentle simmer (do not boil). Stir in the grated Parmesan cheese until it has completely melted into the sauce.

Return the cooked sausage to the skillet. Add the fresh spinach in handfuls, stirring until it has wilted into the sauce. Season with salt and pepper to taste.

While the sauce is simmering, bring a large pot of salted water to a boil. Cook the ravioli according to package directions, usually about 3-5 minutes. Drain well.

Add the drained ravioli directly to the skillet with the Tuscan sauce. Gently toss to coat all the ravioli completely.

Serve immediately, garnished with extra freshly grated Parmesan cheese and a sprinkle of black pepper.