Week 7: Rustic Onion Tart

This week I've been all for simplicity. Boiled corn and new potatoes ... grilled pattypan and yellow squash ... sauteed kale ... you get the idea.

The most ambitious bit of cooking for the week was an onion tart. And by "ambitious" I mean: has more than two ingredients. This is one of those recipes where the individual parts (butter, flour, onion) add up to so much more (sweet, caramelized onions and a flaky, buttery dough). I suspect any kind of yellow or white onion would work in this recipe, giving it year-round possibilities, though my motivation was a large bunch of spring onions from my share.

The tart was equally delicious served warm at supper and eaten cold, straight from the refrigerator. If making tart/pastry dough intimidates you, try this one; it's quite forgiving.

Rustic Onion Tart
(Adapted from The Art of Simple Food, by Alice Waters)

   For the Dough:

1 cup all-purpose flour
1/4 tsp salt
6 Tbsp cold butter, cut into small cubes
1/4 cup ice-cold water

   For the Filling:

2 Tbsp olive oil
2 Tbsp butter
2 lbs onion, thinly sliced (about 6 medium onions)
1/2 to 1 Tbsp fresh thyme leaves
Salt to taste

Stir the salt into the flour. Using a pastry blender, cut the butter into the flour mixture until only a few large pieces of butter remain. Pour in about three-quarters of the water and stir the mixture with a fork until the dough forms clumps, adding the remaining water in small increments as needed. Bring the dough together into a ball, wrap in plastic and flatten the ball into a disk. Refrigerate the dough for 1 hour or more.

Meanwhile, heat the oil and butter in a large skillet over medium heat. Add the onions and thyme, and cook, stirring occasionally, until the onions are very soft and juicy, 20 to 30 minutes. Add salt to taste and continue to cook the onions until they begin to turn golden and caramelize. This could take another 15 to 20 minutes. The liquid should evaporate as the onions cook. Transfer the onions to a bowl (draining any excess liquid, if necessary) and let cool for at least 10 minutes.

Preheat your oven to 375 degrees. Line a large baking sheet with parchment paper. Flour your work surface and rolling pin, and roll out the tart dough to a 14-inch circle. (If the dough is too hard to work with, let it warm up 15 or 20 minutes at room temperature first.) Transfer the dough to the baking sheet and return it to the refrigerator for about 10 minutes to firm up.

Spread the onions on top of the dough, leaving a 1.5-inch border all around. Fold up the border over the onions to create an edge to the tart. Bake the tart for about 50 minutes, or until the crust on the bottom is golden brown. Slide the tart onto a rack to cool. Serve warm or at room temperature.