01 -
In a large skillet over medium heat, melt unsalted butter and cook the sliced onion until softened and translucent.
02 -
Add sliced mushrooms to the pan. Cook, stirring occasionally, until the mushrooms are deep golden and caramelized. Season with salt and pepper during cooking.
03 -
Stir in minced garlic and cook for 1 minute until fragrant.
04 -
Pour in the stock and scrape up any fond from the bottom. Simmer until the liquid is reduced by half.
05 -
Add heavy cream and dijon mustard. Stir well, season to taste, and allow to simmer for 2-3 minutes.
06 -
In a small bowl, blend cornstarch with a tablespoon of water to form a slurry. Pour the slurry into the pan, stirring constantly, and simmer until the sauce thickens.
07 -
Remove from heat. Optionally garnish with freshly chopped parsley or thyme before serving.