Melt the butter in a large skillet over medium-high heat.
Add the sliced mushrooms and season with the salt and black pepper. Cook for 6–8 minutes, stirring occasionally, until the mushrooms have released their liquid and are golden brown.
Stir in the minced garlic and Italian seasoning. Cook for 1 minute, until fragrant.
Reduce the heat to medium. Pour in the white wine and scrape up any browned bits from the bottom of the skillet. Simmer for 1–2 minutes.
In a small bowl, whisk together the heavy whipping cream and cornstarch until smooth.
Stir the cream mixture into the skillet and cook for 3–5 minutes, stirring frequently, until the sauce has thickened.
Remove from the heat, stir in the chopped fresh parsley, and serve immediately.
Notes
This sauce is best served immediately but you can refrigerate the leftovers in an airtight container for up to 5 days. This sauce will thicken when it’s stored so it will need to be thinned out when reheated.