Wash the potatoes thoroughly under running water. Put them in a high-sided pot, fill it with water and bring it over a medium flame. Cook the potatoes for about 20 minutes once the water starts to boil. Drain them, peel them and mash them. Put the mashed potatoes in a bowl. Add the chopped spinach, the eggs and salt and pepper to taste. Line the bottom of a 22/24 cm hinged baking pan with wax paper. Brush the edge with oil and sprinkle it with 30 g of breadcrumbs, then pour in half of the potato and spinach mixture. Level the surface well with a spoon and lay the mild Provolone Valpadana P.D.O. cut into slices on top. Cover with the rest of the mixture, level again and sprinkle with the remaining breadcrumbs. Sprinkle the surface of the gateau with a bit of oil and bake at 180° C for 25 minutes, until golden brown. Remove from the oven, place on a serving plate and serve.