These splendidly rich tarts are my version of French onion galettes. Buttery, flaky pastry crusts are filled with deeply caramelized onions that are generously laced with sage.
The steps to prepare these tarts may seem familiar, but if you take extra care with them, you'll be amazed by the results. Handle the pastry with precision so that it bakes tender, flaky, and shatteringly crisp; spend the time to slowly and thoroughly caramelize the onions until they melt into a golden marmalade; and give the tarts their final baking as close to serving time as possible.
You'll notice the onions are caramelized in a deep saucepan instead of a wide skillet. It makes them easier to stir without flying out of the pan and gives them a chance to soften and stew in their own liquid before it boils away. Once the liquid evaporates, the onions will concentrate and brown, and the balsamic vinegar works to balance the sweetness of the onions and deepen their color. For the best flavor, the whole process should take at least half an hour. Be sure to use regular yellow onions, not Walla Walla, Vidalia, or other sweeter summer onions—they have too much water and do not caramelize well.
Serve the tarts as an hors d'oeuvre at any elegant occasion, or as an accompaniment to a seasonal salad for a light lunch or supper.
Recipe information
Yield
Makes 32 hors-d'oeuvre-size slices
Ingredients
Preparation
Step 1
1. Caramelizing the onions. Peel the onions and cut them in half from root to tip. Cut out the dense core at the root end and slice the onions 1/4 inch thick, again from root end to tip. Cook the bacon, stirring often, in a large (4-quart) saucepan over medium heat until almost crisp. Add the onions, sugar, and salt, and cook, stirring often until they cook down by two-thirds, about 10 minutes. Add 2 teaspoons vinegar, reduce the heat to medium-low, and continue to cook until the onions are an even golden brown and softened to a marmalade consistency, 15 to 30 minutes, depending on the onions. Stir often and scrape up any brown bits clinging to the bottom of the pan. The onions need almost constant stirring near the end to prevent them from sticking and burning. They'll let you know they need attention by giving off a sizzling sound. Stir in the sage, allow them to cool slightly, then taste and season with black pepper and additional salt if needed. If the onions seem overly sweet, stir in another teaspoon of vinegar. (The onions can be caramelized up to 2 days ahead and store covered in the refrigerator.)
Step 2
2. Filling and baking. Preheat the oven to 350°F. Stir the cream and egg into the caramelized onions until thoroughly combined. Divide the filling among the tart shells and spread it evenly with the back of a spoon. Bake in the upper third of the oven until the filling is set, about 15 minutes. The filling should still be soft but not runny. Let cool slightly, then transfer the tarts to a cutting board using a large spatula. Cut each into 8 wedges with the downward pressure of a sharp chef's knife. Serve warm or at room temperature.
Variations
Step 3
For large tarts, prebake 2 10-inch Free-Form Tart Shells. Divide the onion mixture between them and bake the tarts until the filling is set in the center, 20 to 25 minutes. Using a large spatula, transfer them to a cutting board and cut each into 12 wedges.
Herb Substitutions
Step 4
In place of sage, use an equal amount of finely chopped rosemary, marjoram, savory, English thyme, or lemon thyme.
