Slice the mushrooms into 1/4-inch pieces and mince the garlic, and heat the skillet over medium-high heat.

Add butter to the hot skillet and let it foam for about 30 seconds, then add the mushrooms in a single layer.

Cook the mushrooms for 2 to 3 minutes without stirring until golden brown, then stir and cook for another 2 to 3 minutes.

Add minced garlic and cook for 30 seconds to 1 minute, stirring constantly to avoid burning.

Pour in Marsala wine and simmer for 3 to 4 minutes, stirring occasionally, until reduced by half.

Add broth and bring the mixture to a gentle simmer.

Whisk together cornstarch and water in a small bowl until smooth to make a slurry.

Slowly pour the cornstarch slurry into the sauce while whisking, then cook for 1 to 2 minutes until the sauce thickens.

Remove the pan from heat and stir in heavy cream, salt, pepper, and dried thyme, then taste and adjust seasoning before serving.