In a small food processor, add the dates. Add about half of the water and process dates until a paste forms. You will need to scrape down the sides and process several times. If it's too dry, or not coming together add more water and process until it has the spreading consistency of peanut butter. Set aside.
Flour your work surface and unfold the puff pastry on top of it. Sprinkle the pastry lightly with flour to avoid sticking. With a rolling pin, roll out the dough to a little less than a quarter inch thick, trying to maintain the rectangular shape.
Spread date paste evenly over the dough, leaving about one half inch of dough open for sealing dough after you roll it up.
Sprinkle dates evenly with the walnuts.
Arrange the proscuitto in a single layer over the walnuts.
Sprinkle the manchego in an even layer over the proscuitto.
Starting with the longer side of the dough, roll up into a pinwheel. Press slightly to seal the edge. Wrap in saran wrap and chill for at least an hour or overnight.
Preheat oven to 400 degrees. Cover a baking sheet with parchment paper or tin foil. Set aside.
Using a very sharp knife, cut palmiers into 1/2"rounds and place them 1 inch apart on baking sheet.
Bake for 15 minutes until slightly puffed and golden brown. Serve.