Preheat oven to 375.

In a sauté pan over medium high heat, add olive oil and prosciutto or bacon and sauté until crispy. Remove to a small bowl. Add 1 tablespoon olive oil and butter to same pan and add onions, salt and pepper and cook over medium low heat for 15-20 minutes or until the onions are a rich light brown. Remove and cool. Onions can be made the day before and stored in the refrigerator.

On a lightly floured surface, place puff pastry and gently roll into a 10-inch square. Use a pizza wheel or sharp knife and a ruler and cut into four square pieces. With the tip of a sharp knife, lightly score pastry leaving a 1/4-inch border inside to make a crust being careful not to cut all the way through. Then, make slashes on the diagonal all along the crust to make a decoration when it bakes. With a pastry brush, brush the egg around decorated border on pastry and place on baking sheet. Take a fork and prick the bottom of the pastry several times to help avoid pastry from rising too high. Sprinkle cheese over bottom of pastry and bake for 10-15 minutes until they are puffed and golden brown. Remove from oven and allow to cool.

To assemble: Sprinkle caramelized onions over cheese, and sprinkle prosciutto over cheese. Garnish with a chiffonade of fresh basil and serve.