A Delicious Onion Tart

I like to go to the local library and check out scores of cook books. I keep them on my nightstand and I peruse them before bed, noting the recipes I'd like to try. I've been doing this for years. I'm starting to feel like our library is running out of cook books for me. Anyway, this last trip I flipped through some random book and stumbled upon this photo:

Intrigued, I glanced at the recipe to discover that it was an onion tart. Such unusual recipes are right up my alley so I marched right over and checked out the book. (If you're interested, it's Relaxed Cooking with Curtis Stone.) The recipe calls for Taleggio cheese, of which I had none, so I substituted French Brie as it seemed similar. Mr X and I were both rather skeptical of the recipe, fearing that it could potentially end up being a disaster, but it turned out okay and so we dug in - and discovered that it was fantastic! We both loved it and I plan to make it again whenever we have brie or the like on hand. If you're interested, here's the recipe:

Onion Tarts with Taleggio Cheese

Makes 4 servings.

8 tablespoons (120 mL) unsalted butter, room temperature
12 tablespoons (180 mL) sugar
1 very large onion, peeled
1 sheet frozen puff pastry, thawed
1/2 cup (125 mL) balsamic vinegar
4 ounces (100 g) Taleggio cheese, cut into 4 pieces

Spread 2 tablespoons of the butter over the bottom of each of 4 small heavy ovenproof saute pans. Sprinkle 3 tablespoons of the sugar over the butter in each small pan. Cut the onion crosswise into four 1-inch-thick slices, keeping the rings intact. Place 1 onion slice atop the sugar and butter in each small pan. Refrigerate while you prepare the pastry. Unfold the puff pastry sheet and roll it on a lightly floured surface to form a 12-inch square. Cut out for 5-inch rounds from the puff pastry sheet. Drape 1 round over each onion slice and tuck the edges down to cover the onion. Pierce the tops of the pastry rounds with a sharp knife and refrigerate for 20 minutes.

Meanwhile, preheat the oven to 375 F (180 C). Simmer the balsamic vinegar in a small heavy saucepan over medium heat for 10 minutes or until it is reduced by half and coats the back of a spoon. Set it aside to cool. The balsamic reduction will continue to thicken and become syrupy as it cools.

Place the saute pans over medium heat and cook for 5 minutes or until the sugar melts and forms a very pale golden caramel sauce around the tart. Transfer the pans to the oven and bake for about 15 minutes or until the puff pastry is golden brown and the sauce has darkened.
Let the tarts stand for 2 minutes or until the sauce stops bubbling. Swirl the tarts gently to help loosen the onions from the bottom of the pans. Invert each tart onto a plate, using a metal spatula if necessary. Immediately place 1 slice of cheese atop each tart. Drizzle the balsamic reduction around the tarts and serve.