Preheat oven to 400 degrees.
Unfold thawed pastry sheet and roll, using a bit of the flour to make sure it doesn't stick, into a 9x12 inch rectangle.
Slice the sheet into eighteen 3x6 inch squares; cover with a tea towel
In a large bowl, mix together cream cheese and prosciutto; put 2 pieces of each bocconcini into each half jalapeno (use 1 whole bocconcini per jalapeno)
Spoon cream cheese filling into jalapeno halves (on top of bocconcini, smoothing out the cream cheese).
Wrap pastry squares around stuffed jalapenos and arrange on a baking sheet.
Whisk together egg and brush egg mixture over poppers.
Bake for 20 minutes or until golden.
Serve with salsa