Mix the breadcrumbs, garlic, parsley, Parmesan cheese, salt and pepper in the mixing bowl. Drizzle in just enough olive oil to moisten the mixture so it has a sand-like texture. Taste and adjust for seasoning—the mixture should be very savory.

Oil the bottom of a baking dish large enough to hold all the potatoes and mushrooms. Lay down a layer of potato, then a layer of the mushrooms (including some of the reconstituted dried mushrooms if using), season with salt and pepper, and finally top with the breadcrumb mixture. Drizzle some olive oil on top. Repeat these steps until you've used up all the ingredients. But before laying on the final breadcrumb topping, drizzle a bit of water, broth or, if you're using the reconstituted dried mushrooms, some of their soaking liquid, filtered of any grit, down the inside edge of the baking dish, taking care not to upset the ingredients.

Bake in a moderate (18C/350F) oven for a good hour or so, until the potatoes are tender, all the liquid has evaporated and the top is golden brown.

Serve right away.