Preparation:

Step 1:
Start by preparing the caramelized onions. Heat 2 tbsp of butter and 1 tbsp of olive oil in a large skillet over medium heat. Add the sliced onions and a pinch of salt. Cook the onions, stirring occasionally, for about 20-25 minutes, until they become soft and golden brown. If desired, add 1 tsp of sugar to enhance the sweetness of the onions. Once caramelized, set the onions aside.

Step 2:
While the onions are caramelizing, cook the cheese tortellini according to the package instructions. Drain and set aside, reserving a small amount of pasta water to help loosen the sauce later if needed.

Step 3:
In the same skillet used for caramelizing the onions, heat 1 tbsp of olive oil and 1 tbsp of butter over medium heat. Add the sliced mushrooms and cook for 5-6 minutes, until they are browned and tender. Stir occasionally to ensure even cooking.

Step 4:
Add the minced garlic and dried thyme to the mushrooms. Cook for another minute until the garlic becomes fragrant, being careful not to burn it.

Step 5:
Reduce the heat to low and add the fresh spinach to the mushroom mixture. Stir until the spinach wilts, about 1-2 minutes.

Step 6:
Pour in the heavy cream and stir to combine. Allow the cream to heat through, and then add the grated Parmesan cheese. Stir until the cheese melts into the sauce, creating a creamy consistency. Season with salt and pepper to taste.

Step 7:
Add the cooked tortellini to the skillet with the mushroom and spinach sauce. Toss to coat the pasta in the sauce, adding a splash of reserved pasta water if needed to loosen the sauce.

Step 8:
Top the tortellini with the caramelized onions and gently fold them into the pasta. Serve the dish warm, garnished with extra Parmesan cheese and fresh parsley if desired.