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1
For the Onion Filling, place a heavy medium saucepan on medium-low heat and add in the oil.
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2
Add in the onions and thyme, cover and cook till very tender, for about 20 min, stirring occasionally.
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3
Add in the vinegar, bring to a boil and stir till absorbed.
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4
Season with salt and pepper.
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5
(This can be prepared ahead, cooled, covered and set aside at room temperature.)
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6
For the potatoes, carefully cut potatoes into thin, even slices using a knife, a mandoline or possibly a food processor with a slicing blade.
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7
Place in a large bowl of cool water.
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8
(This can be prepared to this point and set aside at room temperature in bowl covered with cool water.
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9
Drain before continuing with the recipe.)
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10
To cook, preheat the oven to 450 degrees.
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11
Dry the liquid removed potatoes well in a lettuce spinner and a clean bath towel.
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12
Line a large baking sheet with parchment paper.
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13
Trace four 5-inch circles on the parchment with dark ink.
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14
Turn the paper over.
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15
If the circles are not visible, redraw them so they are.
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16
Brush the circles lightly with butter.
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17
Overlap the potatoes to cover the bottom of each circle, using the least attractive slices for the center.
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18
Brush lightly with butter.
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19
Season with salt and pepper.
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20
Divide the onions among the centers of the circles.
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21
Flatten onions to 1/8-inch-thick circles using a spatula.
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22
Overlap 1 layer of potatoes around the rim of each circle, leaving part of the onion center exposed.
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23
Brush the top layer of potatoes lightly with butter.
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24
Season with salt and pepper.
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25
Press down on the top layer, sealing it to the bottom layer.
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26
Bake till brown and crisp, for about 30 min.
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27
Press the layers together and neaten edges several times while baking.
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28
To serve, slide a long narrow spatula under the potatoes to loosen them from the paper.
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29
Switch to a broad spatula and carefully transfer the potatoes to 4 small or possibly main course plates, neatening the edges if necessary.
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30
Serve immediately.
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31
This recipe yields 4 servings.
