Preheat oven to 400 degrees.
Open thawed sheets of puff pastry (they are folded in thirds in the package) and place on parchment lined cookie sheets. With a rolling pin, gently roll to an increase of 1 inch. Prick all over with a fork to prevent the pastry from puffing during baking.
Heat oil in a large skillet and cook the onions until soft and golden brown, 12 - 15 minutes. Stir in apples, 1/2 teaspoon salt and 1/4 teaspoon pepper and cook until tender, 2 - 5 minutes.
Spread creme fraiche over pastry within 1/2 inch of the edge. Top with onion/apple mixture (should be a thin layer covering the pastry leaving the 1/2 inch edge free of topping). Bake for 25 - 30 minutes. Remove from oven, sprinkle with cheese and bake an additional 5 minutes. Allow to sit for a few minutes before slicing. Serve warm.
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