Heat the butter in a frying pan over medium-high heat. Add the sliced mushrooms in a single layer and cook for 4-5 minutes without stirring so they get a good golden colour.
Stir the mushrooms and add the minced garlic and thyme. Cook for 1 minute until the garlic is fragrant.
Pour in the double cream and stir well. Simmer for 2 minutes until the cream thickens and coats the mushrooms. Season generously with salt and black pepper.
Toast the bread until golden and butter it lightly.
Spoon the creamy mushrooms over the toast and top with a few sprigs of fresh parsley if you have it.