Preheat oven to 375F. Line 2 baking sheets with parchment paper.
Drain peach juice into a small saucepan.
On lightly floured surface, roll half of puff pastry into a rectangle, measuring about 12x9-inches. Place on a baking sheet and score pastry, about 1/2-inch, all the way around edges. Repeat with remaining puff pastry.
Divide, and then spread sour cream over pastry to cover.
Chop peaches, then sprinkle over sour cream along with onion and prosciutto.
Bake in preheated oven, until pastry is a deep golden brown, rotating baking sheets halfway through, 25 to 35 minutes.
Meanwhile, bring peach juice to a boil. Reduce heat, and then simmer until reduced to a glaze-like consistency, 4 to 7 minutes. Stir in lime juice. Brush over baked pastry (you will not need it all).
Garnish with fresh herbs. Serve with a crisp green salad.
