Begin by cleaning and thinly slicing the mushrooms, ensuring they are even for consistent cooking. Mince the shallots or onions and garlic; gather your other ingredients.

In a large skillet, melt the butter over medium heat. Add the minced shallots or onions along with the garlic. Cook for about 2-3 minutes until soft and translucent.

Now, add the sliced mushrooms to the skillet. Sauté for about 5-7 minutes, stirring occasionally, until golden brown and tender.

Pour in white wine or vegetable broth, scraping the bottom of the skillet to release flavorful bits. Let it simmer for about 3-4 minutes until it reduces slightly.

Lower the heat to medium-low and slowly incorporate heavy cream into the skillet, stirring gently to combine. Allow the cream to warm through for about 2-3 minutes.

Add grated Parmesan cheese to the sauce, stirring until it melts and combines fully. This process should take around 2 minutes.

Season with salt, freshly ground black pepper, and chopped fresh herbs, then stir well to blend the flavors. Remove from heat after 1-2 minutes.

Transfer the sauce over cooked ravioli, garnishing with fresh parsley, extra Parmesan shavings, and a drizzle of truffle oil if desired. Serve immediately.