1teaspoon chopped fresh thyme, plus additional for serving
1sheet frozen all-butter puff pastry, thawed
2teaspoons Dijon mustard
2cups shredded Comté (4 to 6 ounces)
2plum tomatoes, very thinly sliced
Preheat the oven to 400F with a rack in the upper third of the oven. Line a large baking sheet with parchment paper.
Melt the butter in a large skillet and add the onions with a pinch of sugar, salt and pepper. Cook over medium heat until caramelized and golden, about 15 minutes. Add water and scrape up any bits from the bottom of the pan; cook until water is absorbed. Add thyme and transfer to a bowl.
On a lightly floured surface, roll out pastry into a large rectangle, roughly 16 x 13 inches. Cut in half lengthwise. Transfer both pieces to the prepared baking sheet. Brush edges with water and fold over to form a 1/2 inch border. Using the back of a fork, press edges to seal. Prick holes in the bottom of the tart (not on edges) with the fork.
Brush the bottom of each tart with 1 teaspoon Dijon mustard. Divide the caramelized onions among each tart, followed by the shredded Comté. Arrange slices of tomato in an overlapping line down the center of each. Sprinkle with salt and pepper to taste.
Bake in the upper third of the oven for 22 to 25 minutes, or until golden. Cool slightly and sprinkle thyme leaves over the top to garnish. Serve warm or at room temperature.
Recipe courtesy of Comté Cheese Association, Nickie Sizemore