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1
Preheat the oven to 400.
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2
Lightly butter 2 large rimmed baking sheets.
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3
Season the butternut squash with salt and pepper and place it cut side down on one of the baking sheets.
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4
Cover with foil.
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5
Spread the onion slices on the other baking sheet in a single layer.
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6
Season with salt and pepper.
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7
Roast the squash in the lower third of the oven for 1 hour, or until tender.
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8
Let cool, then scoop the flesh into a large skillet and mash until smooth.
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9
Meanwhile, roast the onion slices in the middle of the oven for 30 minutes, turning once, until tender and golden.
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10
Let cool, then coarsely chop.
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11
Cook the squash over high heat, stirring constantly, until any excess moisture is evaporated, about 5 minutes.
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12
Remove from the heat and stir in the onions, Gruyere and thyme; season with salt and pepper.
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13
Transfer the squash to a bowl and refrigerate until chilled.
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14
On a lightly floured surface, roll out 1 piece of the Pastry 1/8 inch thick.
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15
Using a 4-inch round biscuit cutter, stamp out rounds as close together as possible.
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16
Stack the pastry scraps and refrigerate.
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17
Repeat with the second disk of pastry.
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18
When all the scraps are chilled, press them together, reroll and stamp out more rounds.
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19
Discard the remaining scraps.
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20
Preheat the oven to 375.
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21
Working in batches, brush 10 of the pastry rounds with some egg wash. Spoon 1 tablespoon of the squash filling onto the center of each round, fold into a half-moon and press to seal.
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22
Using a fork dipped in flour, crimp the edges.
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23
Transfer the turnovers to the baking sheets.
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24
Brush the turnovers with the rest of the egg wash and bake for 22 minutes, or until golden all over.
