This particular sauce is one of the easiest and most versatile in my repertoire. In fact, because of the way mushrooms are cooked, and the lack of a more saucy base, this recipe yields nothing more then… well, cooked mushrooms. However the nuances of this simple preparation can set the tone for different results, as you can play with ingredients without too many risks.
In Tuscany we do not overwork our foraged mushrooms, if anything we do our best to preserve their original flavor and earthiness by not exceeding cooking time or by seasoning them too much. How easy is it to imagine a toasted slice of sourdough bread topped with the simple mushrooms ragu?
Try changing this sauce by adding some creamy cheese at the very end, right before pouring it onto a warm dollop of freshly made polenta. Or add some tomato sauce and maybe (you did not hear it from me) an extra tab of butter or two, and use the sauce to dress about a pound of fresh potato gnocchi or ravioli. And yes, this could be a side too; imagine it along some chicken cooked in white wine, or some veal scallops.
As far as the ingredients go. When I am at home in Fiesole I tend to cook exclusively with local mushrooms, and Porcini is always my first choice. However, the same suggested weight of your preferred shrooms will provide the same excellent results. Also, this is one of the very few recipes in which I use Speck, which is “Smoked Prosciutto” from the northern mountains of Italy; its flavor is very specific, and any substitution will result in a very different flavor profile. If you cannot find it, I suggest you try replacing it with prosciutto which is less salty than pancetta or guanciale.