Break apart or slice any larger mushrooms so they are all roughly the same size. In a large frying pan, melt the butter, then add the garlic and the mushrooms. Fry for 5 minutes until golden. Be sure not to overcrowd the pan or the mushrooms won't colour.
Add the cannellini beans, crème fraîche and fresh thyme and warm gently for a couple of minutes.
To serve, top the buttered toast with the mushrooms and bean mixture. Garnish with a little more fresh thyme and serve immediately.