Directions

1. Preheat oven to 425. Melt butter with oil in a skillet over medium-high heat. Add onions and thyme, and cook until onions are golden and soft, about 10 minutes.
2. On a lightly floured surface, roll out pastry, and trim to an 8 1/2-by-15-inch rectangle. Place on a parchment-lined baking sheet, transfer to oven, and immediately reduce oven to 400. Bake until pastry begins to rise, about 12 minutes.
3. Arrange onions in a single layer over pastry, leaving a 1-inch border around edge. Top with olives and anchovies if using. Bake for 15 minutes. Reduce oven to 375, and bake until puffed and golden brown, about 15 minutes more (tent with foil if crust browns too quickly). Cut into squares.