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1
Preheat the oven to 400F.
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2
Place a large skillet over medium-high heat with 1 tablespoon of the EVOO.
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3
Season the fish with salt and pepper and sear for a minute on each side.
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4
Remove the fish and reserve.
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5
Add the remaining tablespoon of EVOO to the skillet.
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6
Add the mushrooms and brown for 5 to 6 minutes, then add the leeks and cook until they are softened, 2 to 3 minutes more.
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7
Season the mushrooms with salt and pepper, then add the mustard, cream, and tarragon to the skillet.
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8
Bring up to a bubble, reduce the heat to medium, and simmer until thickened, 3 minutes.
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9
Remove from the heat and let cool.
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10
Roll out the puff pastry with a little flour on a large work area.
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11
Quarter a large sheet or halve two smaller sheets.
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12
Line a baking sheet with parchment paper and arrange the rectangles of dough on it.
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13
Divide the mushroom cream sauce among the rectangles of dough, making a small pile in the middle of each.
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14
Place a piece of seared fish on top of the sauce and fold the edges of the dough up around the fillet.
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15
Trim the excess dough.
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16
Use the egg wash to secure the seam, then place the fish seam side down on the lined baking sheet.
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17
Cut a few slits in the top of each pastry parcel.
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18
Brush them with the egg wash and transfer to the oven.
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19
Bake until the pastry is puffed and golden, about 15 to 20 minutes.
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20
Serve immediately.
