- Rinse the mushrooms and pat them dry. Trim the caps off the mushrooms, then dice the caps into small pieces and set aside. Slice the stems into ¾- to 1-inch “scallops.”
- Melt 1 tablespoon of the butter in a large frying pan over medium heat. Season the scallops with salt and pepper and place them in the pan, flat side down.
- Cook for 2 to 3 minutes, until slightly crispy and golden on the bottom, then flip them. Cook for 2 to 3 minutes on the other side, until crispy and golden, then transfer them to a plate.
- Melt the remaining butter in the pan. Add the leeks and the chopped mushroom caps and cook for about 3 minutes, until the leeks are soft. Add the garlic and thyme and cook for another minute.
- Add the flour and cook, stirring constantly, until the flour is fully incorporated. Add the wine and cook, stirring occasionally, until the liquid has reduced by half, about 3 minutes.
- Add the milk and cook, stirring frequently, until thick and creamy, about 4 minutes. Add salt and pepper.
- Return the scallops to the pan and spoon the sauce over them. Heat them for a minute or two before serving. These are best eaten as soon as they are prepared.