I've rewritten this post a number of times. Each time has been a bit too verbose, a bit too flowery in waxing about the farmers' market, a bit too enthusiastic without really giving you the meat of the recipe. I mean, really. This is a tart. It's nothing we haven't seen before.
That said, this particular tart is a combination of one of Richard's favorite things, which is pie, and one of my favorite things, which is salad. I'm thinking "salad pie" sounds quite oxymoronic, not to mention sort of gross, so we'll keep calling this a vegetable tart. But really, the only reason why this tart is cooked at all once it is assembled is so that you can eat it hot. By all means, if your ingredients are still warm from cooking (or if you've cooked everything far in advance and are cool with eating your tart cold, salad style), you can feel free to fill up the tart shell with all of your goodies and immediately go to town.
Voila, veggie tart!
Chiogga Beet Tart with Ricotta, Walnuts, Caramelized Onions, and Lemon Thyme Makes 1 9-inch tart - Serves 6
Notes: A minimum 1-inch tall tart, quiche, or springform cake pan is recommended for this recipe to make sure your tart shell can hold all of the ingredients. Blind baking the shell is necessary as the ricotta is rather wet and the shell will not properly crisp in the oven if filled while unbaked. Be sure to read the instructions in full, as I gave them to you all mashed up together in the order in which I cook the various elements for the tart (I've emboldened the points at which various things are cooked, Joy of Cooking style, to try and clarify my process)! You can also always roast your beets, sauté your greens, and caramelize your onions ahead of time and then blind-bake your tart shell on the day you plan to bake your fully assembled tart.
3 pounds baby chiogga or yellow baby beets, with greens attached
1 package all-butter puff pastry, such as Dufour, defrosted according to the package instructions (I'll often leave mine in the fridge overnight)
2 medium yellow onions, thinly sliced from top to tail
2 tablespoons butter
2 cloves garlic, minced
1/2 pound whole-milk ricotta cheese (basket ricotta is a good option, as it will be partially drained and less wet than normal ricotta)
1/2 cup coarsely chopped walnuts
2 sprigs lemon thyme or regular thyme, leaves removed from stems
kosher salt, to taste
flaky sea salt, such as Maldon, to taste
Preheat your oven to 400˚F.
Cut the greens away from the beets. Thoroughly wash both the beets and the beet greens, and set the greens aside. To roast the beets, place the beets on a large square of aluminum foil and drizzle with olive oil and sprinkle with a large pinch of kosher salt. Tightly wrap the foil around the beets, and place on a baking sheet to catch any juices that may leak. Roast in the oven for 30-40 minutes, until tender (I test this by piercing a beet with a paring knife).
While the beets are roasting, roughly chop the beet greens, and sauté them in a drizzle of olive oil in a heavy-bottomed pan or skillet over medium heat until they are wilted, but still quite bright green. Season with a pinch of salt, and remove from the heat, and set aside.
Wipe out the beet green pan, and place over medium-low heat to caramelize your onions. Melt the butter in the pan, and add the onions, stirring to coat them all in the fat. Cook, stirring occasionally, until the onions have softened and are translucent, about 15 minutes. Make a well in the center of your onions, add a drizzle of olive oil if the pan is dry, and add your minced garlic to the well. Let the garlic cook for 20-30 seconds, before mixing it into the onions. Add a large pinch of salt to the pan, increase the heat to medium-high, and cook, stirring occasionally, until the onions' color has reached a deep amber. Deglaze the pan with a little water to stir up any lovely caramelized bits on the bottom of your pan, cook for another 30 seconds or so, and remove the onions from the heat.
While the onions are cooking, check your beets. Once they are tender, remove the whole packet from the oven, and let them cool while still wrapped in the foil. Decrease the oven temperature to 375˚F for blind-baking your tart shell.
Flour a baking surface and roll out the puff pastry so that it can easily line a 9-inch x 1-inch tart or quiche pan. Drape the pastry over the pan, and press it into the bottom and sides of the pan. Use scissors or a bench scraper to cut the puff pastry just above the edge of the pan, so the pastry is slightly taller than the pan (it will shrink a little during blind baking, and this will help ensure that it doesn't end up too low in the pan). Place the lined pan on top of a baking sheet for easy maneuvering in and out of the oven.
Prick the bottom of the pastry all over with the tines of a fork. Line the inside of the pastry shell with a piece of parchment paper, and fill with pie weights or dried beans (this, plus the pricking, helps keep the puff pastry from puffing up during blind baking). Bake in your preheated oven for 25-30 minutes, or until the pastry is golden and crisp (start checking it at 20 minutes). Set aside.
Peel your cooked beets, and cut them into wedges. Lightly toss them in a little (1-2 teaspoons) of olive oil along with the lemon thyme.
To assemble your tart, spread the caramelized onions evenly over the bottom of the pastry shell. Spread the ricotta evenly over the onions, and top with the beet greens. Place the beets on top of the greens. Bake at 375˚F for 15-20 minutes, until the tart is hot. Remove from the oven and drizzle with a little more olive oil before sprinkling with a few good pinches of flaky salt. Let the tart sit for a couple of minutes before removing it from the pan and cutting into wedges. Serve hot, warm, or at room temperature.