CAULIFLOWER & CARAMELIZED ONION TART

Steps:

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