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1
Position rack in center of oven; preheat to 425u00b0F
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2
Toss cauliflower with 1 tablespoon olive oil in large bowl.
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3
Spread on large rimmed baking sheet, spacing apart.
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4
Sprinkle with salt and pepper.
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5
Roast 15 minutes; turn florets over.
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6
Continue roasting until tender, about 25 minutes longer.
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7
Cool cauliflower, then thinly slice.
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8
Drizzle with truffle oil; toss.
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9
Reduce oven temperature to 350u00b0F.
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10
Press pie crust onto bottom and up sides of 9-inch-diameter tart pan with removable bottom.
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11
Line pie crust with foil; fill with pie weights.
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12
Bake crust 20 minutes.
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13
Remove foil and pie weights; bake until crust is golden, about 5 minutes, pressing crust with back of fork if bubbles form.
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14
Cool crust.
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15
Maintain oven temperature.
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16
Heat remaining 1 1/2 tablespoons olive oil in heavy large skillet over medium heat.
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17
Add onion; sprinkle with salt and pepper.
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18
Cook until onion is deep golden brown, stirring occasionally, about 40 minutes.
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19
Cool slightly.
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20
DO AHEAD Can be made 1 day ahead.
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21
Store crust at room temperature.
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22
Cover and chill cauliflower and onion separately.
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23
Brush bottom and sides of crust with mustard.
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24
Spread onion in crust.
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25
Arrange cauliflower evenly over.
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26
Set tart on rimmed baking sheet.
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27
Whisk eggs and next 4 ingredients in medium bowl.
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28
Stir in Gruyere.
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29
Pour mixture over filling in tart pan; sprinkle with Parmesan.
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30
Bake until tart is golden and center is set, about 40 minutes.
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31
Transfer to rack; cool 15 minutes before serving.
