Caramelized Onion and Apple Tarts with Gruyère and Thyme

In a large fry pan over medium heat, warm the oil. Add the onions and 1 tsp. 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.

Position 1 rack in the upper third and 1 rack in the lower third of an oven and preheat to 400°F (200°C). Line 2 baking sheets with parchment paper.

In the same pan over medium heat, melt the butter. Add the apples and sugar and stir to coat the apples. Cook, stirring, 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 1/8 tsp. pepper.

Cut the puff pastry into 2-inch (5-inch) squares or diamonds and place on the prepared baking sheets, spacing the squares about 1 inch (2.5 cm) apart. Brush the pastry squares with the egg mixture and place a heaping 1 Tbs. 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 on top, about 25 minutes. Transfer the baking sheets to wire racks and let the tarts cool to room temperature. Serve at room temperature. Makes about 32 tarts.

Adapted from a recipe by Chef Justine Kelly, The Slanted Door, San Francisco.