Melt 2 tablespoons of the butter in a large skillet. Add the leeks and a pinch each of salt and pepper and cook over moderately high heat, stirring occasionally, until softened, about 5 minutes. Add the garlic and cook for 2 minutes longer. Add the remaining 2 tablespoons of butter along with the assorted mushrooms and chopped porcini and cook over high heat, stirring frequently, until the mushrooms have released their liquid. Pour in the wine and cook, stirring frequently, until the liquid has evaporated and the mushrooms begin to brown, about 10 minutes. Season the mushrooms with salt and pepper.