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1
Preheat the oven to 375F.
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2
Line a 12 x 18-inch baking sheet with parchment paper and sprinkle with water.
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3
On a lightly floured surface, roll out the pastry into a 14 x 5-inch rectangle 1/8-inch thick.
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4
Cut the pastry into 4 rectangles.
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5
Place them on the prepared sheet about 1 1/2 inches apart to allow for expansion during baking.
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6
Cover with plastic wrap and refrigerate for 20 minutes, or until chilled.
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7
Beat the egg yolk with 2 tablespoons cold water.
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8
Brush the tops of the chilled pastry lightly with the egg wash. Bake for 20 minutes, or until puffed and golden.
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9
Meanwhile, in a large skillet, melt the butter over medium heat.
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10
Add the mushrooms and season with salt and pepper.
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11
Cook, stirring from time to time, just until the mushrooms give off their liquid, about 5 minutes.
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12
Pour off the cooking liquid into a saucepan.
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13
Keep the mushrooms warm.
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14
Cook the liquid over low heat until reduced to about 1 tablespoon.
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15
Set aside.
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16
In a medium saucepan of lightly salted simmering water, poach the asparagus for 5 to 7 minutes, or until crisp-tender.
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17
Drain and keep warm.
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18
Prepare the sauce: Place the wine, orange juice, and vinegar in a small nonreactive heavy saucepan over medium heat and slowly bring to a simmer.
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19
Continue to simmer until the mixture is syrupy and reduced to about 2 tablespoons.
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20
Remove the pan from the heat and whisk in about 2 tablespoons of the butter pieces.
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21
Return to low heat, and whisking constantly, add the remaining butter piece by piece.
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22
Whisk in the reduced mushroom liquid and optional demi-glace.
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23
Set aside on the warm side of the stove.
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24
Using a serrated knife, carefully slice each pastry in half lengthwise.
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25
Place each bottom slice on an individual warm plate.
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26
Divide the mushrooms over each, then add the asparagus spears.
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27
Coat the asparagus with the sauce.
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28
Place the top pastry over the asparagus and serve immediately.
