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1
Preheat oven to 400 degrees F.
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2
Using a mandolin or super-sharp knife, cut onion into paper thin slices.
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3
Clean and slice the mushrooms.
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4
Heat 1 tablespoon oil in a skillet over medium heat; add onion and saute until caramelized.
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5
Transfer to a bowl and set aside.
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6
Heat remaining teaspoon of oil in skillet over medium-high heat.
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7
Add mushrooms and saute until they release all their liquid and most of it boils away, should take about 5 minutes.
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8
Combine caramelized onions with mushrooms and saute together briefly; season with salt and pepper.
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9
Remove the pan from heat.
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10
Unfold puff pastry onto a floured surface; cut in half lengthwise to form 2 long rectangles.
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11
Gently roll out each rectangle to approximately 5 by 14 inches and place on cookie sheet.
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12
Trim edges by 1/4-inch strips all around; set strips aside.
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13
Break 1 egg into a small bowl; beat slightly.
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14
Brush edges of pastry with some of the egg.
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15
Use trimmed strips to make a raised border on each.
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16
Brush entire surface with remaining beaten egg.
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17
Prick the interior of pastry all over with a fork.
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18
Bake until pale gold, about 10 minutes.
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19
If pastry has puffed up inside edge, press it down gently.
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20
Set aside.
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21
Meanwhile, combine remaining eggs with 6 ounces goat cheese and blend until smooth.
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22
Spread the mixture onto pastry.
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23
Return to oven and bake just until set, about 4 minutes.
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24
Add the thyme to the mushroom mixture.
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25
Remove cookie sheet from oven and spread with thyme-mushroom mixture.
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26
Crumble remaining cheese on top.
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27
Just before serving, broil tarts on low heat for 2 to 3 minutes, until tarts are warm and cheese softens.
