This savory Sweet Potato, Spinach, and Caramelized Onion Tart with Balsamic Reduction makes an elegant starter for Shabbat or holiday meals. The caramelized onions are the star ingredient, and though they're simple to make, they do require patience. Cook them slowly over low heat, and you'll be rewarded with a lush, sweet pile of meltingly soft onions.
And here's an insider tip: though knowing how to make a balsamic reduction is a useful skill to have in your kitchen arsenal, there is a great kosher alternative to the DIY option. The Date Lady, a specialty food purveyor dedicated to all things, well, date, makes a fabulous date balsamic vinegar. It's syrupy and complex, and perhaps the closest approximation of an Aceto Balsamico Tradizionale available on the kosher market today.
Dairy Variation: If you're making a dairy meal, goat cheese or Parmesan would make an excellent addition to this vegetable tart. You can also opt for an all-butter puff pastry, such as Dufour Pastry Kitchens' Kof-K certified product.
- 1 sheet puff pastry (pareve, frozen, thawed)
- 3 tablespoons olive oil (extra-virgin, divided)
- 2 small sweet potatoes (about 4 ounces each, peeled and cut into 1/4" thick rounds)
- 1 medium onion (about 8 ounces, peeled, halved, and very thinly sliced)
- 3 cloves garlic (peeled and finely chopped)
- 10 ounces spinach (frozen, chopped)
- 1/4 cup balsamic vinegar
- 1 tablespoon honey
- 1 pinch salt (sea)
- 1 pinch black pepper (coarsely ground)
1. Preheat the oven to 425° F. Line a sheet pan with parchment paper or foil. In a large bowl, toss the sweet potato rounds with 1 tablespoon of olive oil. Spread the sweet potatoes in a single layer on the prepared sheet pan. Roast the potatoes until they are tender and the undersides begin to develop brown speckles, about 15 minutes. Gently turn the sweet potatoes and roast for 3 to 5 minutes more.
Remove from the oven, season to taste with sea salt and black pepper, and set aside.
2. Warm 1 tablespoon of olive oil in a heavy skillet set over medium-high heat. (A cast iron skillet is ideal.) Add the onions and sauté until they begin to turn soft and translucent, about 5 minutes. Sprinkle the onions with a pinch of salt. Lower the heat to medium-low, and continue to cook the onions, sautéing every few minutes, until they are a deep golden brown, about 30 minutes. (Tip: Keep an eye on the onions, and stir whenever the ones in closest contact with the pan start to turn a deeper brown. This will help you achieve even caramelization without burning the onions.)
3. Use tongs to transfer the caramelized onions to a dish. Add 1 tablespoon of olive oil to the same skillet you used to cook the onions. Add the garlic and spinach and sauté until the spinach is cooked through, about 5 minutes. Remove from the heat, season to taste with sea salt and black pepper, and set aside.
4. Place the puff pastry sheet on the prepared baking sheet and unfold. Using a sharp knife, trim a 1/4" strip from each side of the puff pastry sheet. Carefully place the strips atop the edges of the large pastry sheet to create a frame for the filling.
5. Spread the sweet potato rounds evenly over the puff pastry. Spread the spinach over the sweet potatoes so it reaches the inside edge of the pastry frame. Top evenly with the caramelized onions.
6. Bake the tart in a preheated oven until the pastry is golden brown, about 25 to 30 minutes.
7. While the tart is baking, make the reduction. Place the balsamic vinegar and honey in a small saucepan. Bring to a boil, then reduce the heat to low. Allow the vinegar to cook down, stirring occasionally, until it thickens slightly and is reduced by about half. Remove from the heat and set aside.
8. When the tart has finished baking, remove it from the oven and allow to cool slightly. Drizzle with the balsamic reduction just before serving. Enjoy!