Cauliflower and Caramelized Onion Tart

Nothin' better than melted Gruyere.

Cauliflower and Caramelized Onion Tart
Adapted from Smitten Kitchen and my tried-and-true crust

Ingredients: 

Crust

1 1/2 C. Whole-Wheat Flour
1 t. Salt
1 t. Sugar
1/2 C. (1 stick) chilled unsalted Butter, cut into 1/2-inch cubes
1 large Egg
1 t. cold Water
1 large Egg White, lightly beaten 

Filling
1 lb. head of Cauliflower (about 1 small head), cut into 1-inch flowerets
3 1/2 T. Olive Oil
1 1/2 T. Cayenne Pepper
1 large Onion, halved lengthwise and thinly sliced
1 T. Dijon mustard (optional, see instructions)
2 large Eggs
1/2 C. Half-and-Half
1/4 C. Sour Cream
1/4 t. Ground Black Pepper
Pinch of ground Nutmeg
1 1/2 C. grated Gruyère cheese

Directions:
For crust:
Blend flour, salt, and sugar in processor.  Add butter; using on/off turns, process until coarse meal forms. Whisk 1 egg and 1 teaspoon cold water in small bowl; add to flour mixture.  Using on/off turns, process just until moist clumps form.  Transfer to work surface and knead gently until dough comes together, about 4 turns.  Form into ball; flatten into disk. Wrap in plastic and chill from 1 hour to 1 day.

Butter 9 1/2-inch round pie pan.  Transfer dough to pan, pressing onto bottom and up sides of pan; trim any excess dough.  Chill 1 hour.

Preheat oven to 400 degrees.  Butter large square of foil and press, butter side down, onto crust. Fill with pie weights or dried beans.  Bake 20 minutes.  Remove foil and weights.  Using fork, pierce bottom of crust all over (about 10 times).  Bake until golden, about 10 minutes.  Brush lightly with egg white.  Cool.

For filling:
Preheat oven to 425 degrees.  Toss cauliflower in large bowl with 2 tablespoons olive oil, 1 tablespoon cayenne pepper, and salt and pepper to taste.  Spread on rimmed baking sheet and roast 15 minutes before turning florets over and roasting until brown and tender, about another 15 minutes. Cool cauliflower and thinly slice.  Reduce temperature to 350 degrees.

Heat remaining 1 1/2 tablespoon olive oil in a heavy large skillet over medium-low heat.  Add onion, sprinkle with salt and pepper and cook until onion is a deep golden brown (about 30 minutes), stirring occasionally. 

Original recipe suggested spreading the bottom and sides of crust with mustard, which tasted a little sweet in the final product to me.  Spread onion over crust.  Arrange cauliflower over the onion.  Whisk eggs, nutmeg, sour cream, half-and-half, and pepper in a medium bowl.  Stir in 1 cup Gruyere.  Pour mixture over filling.  Finish sprinkling 1/2 C. Gruyere over top.  Bake until quiche is golden and center is set, about 40 minutes.  Transfer to rack and cool 15 minutes before serving.