The seedling of an idea for this recipe started while I was making cheddar cheese crackers for the kids. The thought occurred that it might be an interesting base for a tart crust.
As I wandered through the farmers' market later that day, in search of some "late winter" inspiration, a bunch of humble onions set the ball rolling. It was at the moment I knew I wanted to recreate the flavors of a French onion soup into my tart. While the directions seem long, it really does come together effortlessly, and well worth the time it takes to caramelize the onions. —Jennifer Perillo
Test Kitchen Notes
WHO: Jennifer Perillo is a mother, a food editor, and a blogger at In Jennie's Kitchen.
WHAT: French onion soup, re-imagined and re-packaged in tart form.
HOW: A filling of caramelized onions, thyme, Swiss cheese, sherry vinegar, and egg is poured into a whole wheat crust and baked.
WHY WE LOVE IT: The cheesey, whole wheat crust is tender and lovely, a perfect foil for the sweet, onion-loaded filling. The sherry vinegar keeps the whole tart balanced. And just like the soup, this tart is deeply satisfying...but not so rich that you can't eat two slices. —The Editors
To make the filling, heat the olive oil in a heavy-bottomed pot over medium-high heat. Add the onions and saute for 2 minutes. Cover pot, reduce heat as low as it can go without shutting off, and let cook until onions have cooked down and released a lot of their liquid, about 20 minutes.
Meanwhile, prepare the crust. Add the flour, salt, and paprika to the bowl of a food processor. Pulse once or twice to mix the dry ingredients. Add the cheese and butter, then pulse a few times until it forms a sandy-looking mixture. Add 1 tablespoon of seltzer, pulse again until a rough ball of dough comes together. If the mixture is too dry and crumbly, add more seltzer 1 teaspoon at a time (you may not need the entire 2 tablespoons), and continue to pulse until you have a ball of dough. Turn the dough out onto an unfloured counter, flatten and shape into a disk. Wrap in plastic wrap and chill for 30 minutes.
Preheat the oven to 400ºF.
Remove cover from the pot of onions, raise heat to medium, add the thyme and season with salt and pepper. Let the onions cook, stirring occasionally to scrape the browned bits from the bottom of the pot, until onions turn golden brown, about 30 to 35 minutes. When onions are golden and very tender, stir in the sherry vinegar. Remove from heat and, using a slotted spoon, transfer onions to a medium bowl.
Place the chilled dough between two sheets of parchment paper, and roll it into a 13-inch circle. Fit dough into a 9-inch ungreased springform pan. Fold down sides of dough, leaving a 1-inch high crust.
To finish the filling, add the egg and cheese to the bowl with the onions. Stir to mix well. Pour mixture over the tart crust and spread to the edges using a rubber spatula. Bake for 25 minutes, until slightly puffed and golden. Remove from oven and let cool for 5 to 10 minutes before slicing.
Jennifer Perillo is the Consulting Food Editor at Working Mother magazine, and a regular a contributor to Relish Magazine and FoodNetwork.com. She shares stories about food, family and life at her blog In Jennie's Kitchen and in her debut cookbook, Homemade with Love: Simple Scratch Cooking from In Jennie's Kitchen (Running Press 2013).