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1
Preheat oven to 400F.
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2
Butter 13x9x2-inch glass or ceramic baking dish.
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3
Melt 6 tablespoons butter in large nonstick skillet over medium heat.
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4
Add onions, thyme, and 2 teaspoons salt; saute until onions are translucent, about 10 minutes.
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5
Increase heat to medium-high; saute until onions are tender and begin to color, about 8 minutes longer.
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6
Remove from heat.
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7
Add remaining 6 tablespoons butter, 2/3 cup water, wine, and sugar to skillet; stir and swirl skillet to combine.
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8
Bring to boil.
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9
Cool onion mixture to lukewarm.
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10
Combine potatoes, apples, remaining 2 teaspoons salt, and onion mixture in large bowl; toss gently to blend.
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11
Transfer to prepared baking dish, spreading evenly.
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12
Cover dish with parchment paper, then cover with foil, shiny side down.
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13
Bake gratin until potatoes are tender, about 55 minutes.
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14
Uncover and bake until top browns and juices bubble thickly, about 20 minutes longer.
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15
(Can be made 6 hours ahead.
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16
Let stand uncovered at room temperature.
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17
Rewarm, loosely covered with foil, in 300F oven for 20 minutes.)
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18
Let gratin stand 15 minutes before serving.
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19
This gratin is unusual for having no cream or cheese letting the lovely seasonal flavors of the produce shine through.
