Lynne Rossetto Kasper calls this dish the "lasagna of mashed potatoes."  It is basically crushed potatoes mixed with Parmigiano, salami and peas, layered in a casserole with a filling of mozzarella and browned onions.

3 pounds Yellow Finn or red-skinned potatoes
Water to cover
Extra-virgin olive oil
1 medium onion, cut into ¼ inch dice
Salt and freshly ground pepper
1 large clove garlic, peeled
1 large clove garlic, minced
3-4 1-inch thick slices country bread, torn into bite-sized pieces
4 Tablespoons unsalted butter
1 cup freshly grated Parmigiano-Reggiano cheese
1/3 cup milk
5  1/8-inch-thick slices soppressata or other good-tasting salami, cut into ¼-inch dice
1-1/3 cups tiny frozen peas, defrosted
½ pound fresh mozzarella in liquid, drained and sliced ¼-inch thick

 1. Place the potatoes in a 4-quart pot, cover with water, and simmer 25 minutes or until tender.

 2. While the potatoes cook, lightly film a 10-inch skillet with olive oil and heat over medium-high heat.  Quickly brown the onion, seasoning with salt and pepper.  Take off the heat and turn the onions into a bowl.  Wipe out the skillet with a wad of paper towels and set aside.

 3. Turn on the food processor, drop in the garlic, then the bread, and process until the bread is in coarse crumbs (about ½-inch pieces).  Film the skillet again with oil.  Add the bread and stir over medium heat, sprinkling with salt and pepper, about 5 minutes, or until pale gold.  Turn out onto a sheet of foil and cool.

 4. Preheat the oven to 400° F.  Oil an 8-inch square baking dish or pan.  Slice the butter into a large bowl.  Drain the potatoes, peel, and add to the bowl.  Mash with a large fork, blending in the Parmigiano, milk, and salt and pepper to taste.  The potatoes should be lumpy.  Fold in the salami and half the peas.  Spread half the potatoes in the baking dish.  Top with the remaining peas and the onions, then the sliced mozzarella.  Cover with the rest of the potatoes.  (At this point, you can cover and refrigerate the casserole overnight.  Bring to room temperature before baking.)

 5. Bake about 30 minutes or until the casserole is hot.  Top with bread crumbs, pressing them into the potatoes a bit.  Bake another 10 minutes.  Serve hot, cutting into 8 or more squares.

 (from The Italian Country Table, by Lynne Rossetto Kasper)

Dorothy's Notes & Deviations
I made this recipe for the Italian cooking event held by the Twin Cities MN Ring of Recitopia on September 8, 2001, at Mickie's home.  These are my notes:

Potatoes – I used Yukon Gold, large size.
Garlic – why this calls for one whole clove and one minced, I don't know.  I minced the whole batch.
Butter – I used regular, not unsalted.
The fresh mozzarella I found was not in liquid (found at Byerly's).

I overestimated the quantity of potatoes when I doubled the recipe for our gathering at Mickie's.  I would either cut down on the potatoes or use more of the filling ingredients (onions, peas, salami, cheese) if I were to make this again (which I probably will, since I am the original "potato girl!").