01 - Heat butter in a large skillet over medium heat until fully melted.
02 - Add finely chopped shallot and cook for 1 to 2 minutes until translucent.
03 - Stir in minced garlic and sauté for 30 seconds until fragrant.
04 - Add sliced mushrooms and cook for 6 to 8 minutes, stirring occasionally, until moisture releases and mushrooms brown.
05 - Pour in white wine if using, and simmer for 2 to 3 minutes until most liquid evaporates.
06 - Incorporate vegetable broth, heavy cream, and whole milk; stir thoroughly to combine.
07 - Add thyme, salt, and pepper. Reduce heat and simmer gently for 5 to 7 minutes, stirring occasionally until sauce thickens.
08 - Taste the sauce and modify seasoning as necessary.
09 - Remove from heat and sprinkle chopped fresh parsley if desired before serving.