Provençal Onion Tart

Direction :

Heat oven; cook onions:
Preheat oven to 425°F. Melt butter with oil in a medium skillet over medium-high heat. Add onions and thyme, and cook, stirring occasionally, until onions are golden and soft, about 10 minutes.
Roll out pastry:
On a lightly floured surface, roll out pastry to an 8 1/2-by-15-inch rectangle, trimming edges to make them straight.
Transfer to oven, reduce temperature, and bake:
Place on a parchment-lined baking sheet, transfer to oven, and immediately reduce oven temperature to 400°F. Bake until pastry just begins to puff, about 12 minutes.
Arrange toppings over pastry; bake 15 minutes:
Arrange onions in a single layer over pastry, leaving a 1-inch border all around. Top with olives and anchovies (if desired). Bake 15 minutes.
Reduce oven temperature and continue to bake:
Reduce oven temperature to 375°F, and continue baking until tart is puffed and golden around the edges, about 15 minutes more (tent with foil if crust browns too quickly). Let cool slightly before cutting into small squares and serving.