Onion Tarts

Free-Form Tart Shells, made from Flaky Pastry Dough (4 7-inch or 2 10-inch shells)
2 ounces bacon (2 slices), finely diced
2 pounds yellow onions (3 large or 4 medium), sliced
1 teaspoon sugar
1/2 teaspoon salt
2 to 3 teaspoons balsamic vinegar
2 tablespoons finely chopped fresh herbs (sage, thyme, rosemary, marjoram, savory, or combination)
Freshly ground black pepper
1/4 cup heavy cream
1 large egg

In a large (4-quart) saucepan, cook the bacon over medium heat until almost crisp.  Add the onions, sugar, and salt, and cook, stirring often, until the onions are cooked 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.  Stir in the chopped fresh herbs, allow the mixture to cool slightly, then taste and season with black pepper and additional salt if needed.  Another teaspoon of vinegar can be added if the onions seem overly sweet.  (The onions can be caramelized up to 2 days ahead and stored, covered, in the refrigerator.)

Heat 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 for 7-inch tarts or 20 to 25 minutes for 10-inch tarts.  The filling should still be soft but not runny.  Let tarts cool slightly, then ptransfer the tarts to a cutting board using a large spatula.  Cut each into 8 or 12 wedges with a sharp chef's knife.  Serve warm or at room temperature.  

Makes 4 7-inch or 2 10-inch tarts.

From The Herbfarm Cookbook by Jerry Traunfeld

Note: To make without bacon, use 3 tablespoons of extra-virgin olive oil to caramelize the onions.