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1
Preheat oven to 400 degrees.
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2
For the crust: In a food processor, combine the flour, sugar and salt in the bowl and pulse to blend. Add the butter and pulse. Add the water a little at a time and pulse until the dough just begins to come together in a rough mass.
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3
Transfer the dough to a floured work surface and roll into a 13-inch disk, about 1/4″ thick. Fold over the edges of the dough, about 1″ around, and crimp to seal. Transfer to baking sheet and refrigerate until ready to use.
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4
For the filling: Melt butter in a large skillet over medium heat. Add salt and combine, then add onions. Cook for 15-20 minutes, stirring frquently, until carmelized on all sides.
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5
Add the wine and reduce until syrupy, about 6-8 minutes.
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6
Transfer the pan to the oven and roast for 10 minutes.
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7
Remove the pan from the oven and place the refrigerated dough on top of the onions. Prick the surface to let air escape.
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8
Return the pan to the oven and bake until crust is golden brown, about 35 minutes.
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9
Remove the pan from the oven and let stand for 5 minutes.
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10
Place a serving platter upside down on top of the pan and turn both upside down together. Lift off the pan, leaving the onion tart on the serving dish. Serve immediately!
