Preheat the oven to 375˚F.
Place the stack of phyllo on a parchment-lined baking sheet.
Fold all but the bottom two over like turning the pages of a book, and brush in between the layers with some melted butter or oil—don’t worry about covering it completely.
Brush between every two sheets, doing it on both sides.
Fold the edges of the stack over by about half an inch and spread the top with pesto or drop it in small spoonfuls.
Sprinkle with tomatoes and cheeses and top with prosciutto.
Bake for 20 minutes, or until the pastry is golden and crisp and the toppings are bubbly. Cut into squares or rectangles to serve.