Caramelized Onion and Apple Gruyere Tarts

These caramelized onion and apple tarts are topped with gruyere, thyme, and chives, and all of this goes on top of puff pastry for the tart.  This is an easy yet elegant appetizer. These appear nearly every year at my Christmas party and pair quite well with sparkling wine!

The longer you caramelize onions, the better they are.  Using tart apples really makes the caramelized onions pop in flavor, and the nutty Gruyere only enhances it! If you have more time and can caramelize the onions for closer to an hour, your taste buds will be rewarded. :) These can be made ahead and can be served at room temperature.

Caramelized Onion and Apple Gruyere Tarts
Yields 36 tarts

Ingredients: 
2 tbsp. extra virgin olive oil1 1/2 lb. (750 g) sweet onions, halved and thinly sliced2 tbsp. unsalted butter
1 lb. Granny Smith apples, peeled and sliced 1/8 inch thick
1 tsp. granulated sugar
1 1/2 oz. Gruyere cheese, grated
2 tbsp. Minced fr sh chices
1 tsp. Chopped fresh thyme
1 package 1 lb. frozen puff pastry dough, thawed
1 egg beaten with 2 tbsp. Water
Salt and ground pepper, to taste

Directions:
Position 1 rack in the upper third and 1 rack in the lower third of an oven.  Preheat to 400°F.  Line 2 baking sheets with parchment paper.

In a large fry pan over medium heat, warm the oil.  Add the onions and a few sprinkles of  salt and cook, stirring occasionally, until the onions are golden brown, about 30 minutes. Transfer to a large bowl and let the filling cool to room temperature.

In the same pan over medium heat, melt the butter.  Add apples and sugar, and stir to coat the apples. Stir and cook, until the apples are just starting to caramelize and have softened, about 10 minutes. Transfer to the bowl with the onions and stir in the cheese, chives, thyme, and a few sprinkles of pepper.

Cut the puff pastry into 2-inch squares and place on the prepared baking sheets, spacing the squares about 1 inch apart. Brush the pastry squares with the egg mixture and place a heaping 1 tbsp. topping in the center of each square. Season with salt and pepper.

Bake, rotating the baking sheets from top to bottom and front to back halfway through baking, until the pastry is crisp underneath and golden brown, about 25 minutes. Transfer the baking sheets to wire racks. Let the tarts cool to room temperature. Serve at room temperature. 

Source: Williams-Sonoma Wine Club