Melt ⅓ of the butter in a frying pan with the garlic clove and sauté for about a minute. Add the sliced mushrooms and a pinch of salt. Cook over medium heat for around 10 minutes, or until the liquid has evaporated and the mushrooms are dry. Stir in the parsley, remove from the heat, and let the mixture cool.

Peel the potatoes and cut them into thin slices about 2 mm – 0.1 inch thick. Place them in a pot, cover with water, add salt, and bring to a boil. Simmer for 5 minutes after the water starts to boil. Drain well and set aside to cool.

In another pan, melt another ⅓ of the butter over low heat. Add the breadcrumbs and sauté for a couple of minutes, stirring constantly so they don’t burn. Remove from the heat and set aside.

Grill or broil the speck (or bacon) for 2–3 minutes, until crisp. Transfer to kitchen paper to absorb any excess fat. Once cool, break it into small pieces.

When the pizza dough has doubled in size, divide it into 4 balls and roll each one into an oval, about 0.5 cm – 0.2 inches thick. Spread ¼ of the breadcrumb mixture over each oval, then layer the potatoes, mushrooms, Asiago, and speck on one half of each. Fold the dough over to enclose the filling and crimp the edges firmly with your fingers to seal. Arrange the calzoni on a baking tray lined with baking paper. Melt the remaining butter and brush it over the tops.

Bake in a preheated oven at 240°C – 465°F for about 20 minutes, or until puffed and golden. Serve warm.