Creamy and so delicious, this vegan French Onion Tart has all of the texture and flavor you'd expect in a traditional quiche except it's completely egg-free and dairy-free! The mouthwatering vegan quiche filling sits over a layer of vegan cheese, all settled into a delicate, flakey crust.
In a large bowl, whisk the flour, salt and baking powder together. Add the cubes of vegan butter and shortening. Using a pastry cutter or a fork, cut the vegan butter and shortening into the flour until the fats are about the size of green peas.
Pour in 3 tablespoons (45 mL) of the ice water into the flour mixture, stirring with a silicone spatula or large spoon. Add more (a tablespoon at a time) water only until the dough barely holds its shape when pressed between your fingers and released. The dough should be shaggy and not sticky. If you add too much water, the pastry won't be as delicate or flaky once baked.
Place the pastry dough onto a lightly floured work surface. Gather and press the dough into a rough rectangle about 1/2” (1.3 cm) thick. Like you would a letter, fold the dough in thirds handling the dough as little as possible so the warmth of your hands doesn't melt the fat. Repeat this four times. With each series of folds, the dough will become more pliable. You'll see streaks of fat through the dough and this is a good thing! Wrap the dough tightly in plastic wrap and chill for an hour or up to 3 days.
About 30 minutes before baking, preheat the oven to 400°F/200°C/gas 6.
Remove the pastry from the fridge. On a lightly floured work surface, use a floured rolling pin to roll the pie dough out from the center to form a 12” (30 cm) circle for a 10” (25.4) pie dish*. As you roll, check occasionally that the dough is not sticking to the work surface, adding more flour as necessary.
Place the rolling pin in the middle of the pastry and fold the dough in half over the rolling pin to lift it. Lower the pastry over the pie plate, unfold the pastry. Gently lift and drape to adjust the pastry but do not force or stretch it.
Trim the dough if necessary so there is about 3/4” overhang. Fold the overhanging dough under the pie crust and flute or shape the edges as desired. Prick the sides and bottom of the pie crust with a fork.
Line the pastry with parchment paper, and fill with dried beans, pie weights or granulated sugar. Bake in the preheated oven for 12 minutes or until the bottom of the crust is just starting to brown (you'll only be able to tell if you're using a glass pie plate, otherwise just go by the timer.) Reduce the oven temperature to 325°F/165°C/gas 3.
For the Tart Filling:
In a large heavy bottomed pot of skillet, the olive oil over medium high heat. When the oil is shimmering, add the onions.
Reduce the heat to medium or medium-low. Stir the onions every 3-5 minutes to prevent sticking, but not so often that they don’t get a chance to brown. Scrape the bottom of the skillet to lift any browning to prevent burning. If the onions are browning quickly on the edges or are sticking, try turning the heat down a bit or adding a splash of water. This is a slow process which will take 30-50 minutes. Once the onions are caramelized to a rich golden brown color, stir in the soup stock, balsamic vinegar and thyme, scraping the bottom of the pot with a wooden spoon to lift any stuck bits. Turn up the heat and simmer until the moisture has evaporated. Remove the onions from the heat.
To a blender, add the silken tofu, soaked cashews, nutritional yeast, mustard powder, nutmeg, salt and pepper. Blend until completely smooth, scraping down the sides as necessary. This may take a few minutes depending on the how powerful your blender is.
In a large bowl, combine the caramelized onions and the tofu mixture, stirring well.
Sprinkle the vegan cheese evenly over the parbaked pastry. Pour the onion tofu filling over the cheese and smooth out the top with the back of a spoon. Place a baking dish on the bottom rack of your preheated oven and fill it with water. This will create some steam to help prevent the quiche top from splitting during baking.
Bake the quiche in the preheated oven for 35-40 minutes, rotating the tart in the oven once during baking for even cooking. When ready, the tart will be light brown on top and set in the middle.
Let the tart rest for 10 minutes before slicing and serving. Serve with fresh green salad, or as desired.
Store leftovers in an airtight container for up to 5 days. Reheat in the oven preheated to 350°F/177°C/gas 4. The time will vary depending on how much tart you're reheating.
This recipe was tested using a 10.5" (26.7 cm) tart dish. Other tart or pie pans of similar sizes (e.g. 9" is common) will work although depending on their depth, you may have extra filling. For smaller tart pans, the quiche may cook a bit faster so start checking for doneness around 30 minutes. Use only vegan butter sticks. Tub style vegan butter has a higher water content than baking sticks which can effect the quality of the pastry.