1. Thaw your puff pastry on the counter for a couple of hours or overnight in the fridge.
2. Unroll your puff pastry and lightly drizzle truffle oil on the base of the pastry. Next, layer on the gruyere leaving roughly 1.5 inches of unexposed crust to be folded over later.
3. In a sauce pan over medium high heat, combine olive oil, shallot and sliced mushrooms. Sauté until the mushrooms are softened but not fully cooked.
4. Place your sautéed mushrooms and shallots on top of the cheesed puff pastry. Fold over the uncheesed crust making sure to tuck the puff over any cheese or mushrooms to avoid them escaping while baking.
5. If you are making the tart to eat in the same day, place the unbaked dish on parchment paper in the fridge for 15 minutes. If you are not making the puff to eat on the same day, place on parchment paper and on a baking pan with a lip on it. Tightly seal with plastic wrap and freeze. Will keep for 2-3 days.
6. Preheat oven to 425°F.
7. Take your puff out of the fridge and place on parchement paper and a cookie sheet. Lightly brush the crust with the egg wash. Lightly salt and pepper the crust and the puff interior to taste.
8. Bake in the oven for 10 minutes or until you see that the crust has puffed and the edges have started to turn lightly golden brown.
9. Reduce your oven to 375°F and continue baking for 15 minutes. You want to make sure that the pastry is a deep golden brown before you pull it out.
10. Cool and top with freshly minced chives to serve your dish. I don't recommend cutting this before it has proper time to set, otherwise you and your guests will be fighting over the string of gruyere that is being pulled apart from the puff pastry.

Recipe Notes

This dish could be easily elevated with the addition of cured meat. Tiny chunks of ham or thin slices of spec would be a nice addition to this mellow mushroom tart. If adding cured meat, be careful not to over salt your puff as the meat will add an extra salty component.

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