Directions

1. If using baby leeks, halve lengthwise and trim to about 3 inches long. If using regular leeks, cut crosswise into 3-inch pieces; halve each piece lengthwise, then cut into 3/8-inch-thick strips (about 5 cups). Rinse well, and drain; set aside.
2. Melt butter with oil in a medium saute pan over medium heat. Add leeks and 1/4 teaspoon salt; cook, stirring occasionally, 5 minutes. Reduce heat to medium-low; cover, and cook, stirring occasionally, until leeks are tender but not browned, about 15 minutes. Stir in thyme. Leeks can be refrigerated in an airtight container up to 1 day; bring to room temperature before assembling tart.
3. Cut or roll out pastry to a 6-by-14-inch rectangle; place on a parchment-lined baking sheet (reserve remaining pastry for another use). Score a 3/4-inch border. Brush with egg wash; sprinkle with Parmesan. Refrigerate 30 minutes.
4. Preheat oven to 375. Bake pastry until golden, 10 to 15 minutes. Remove from oven, and press center area with a met��al spatula. Arrange leeks end to end in rows within border of pastry. Scatter olives over leeks. Bake until crust is golden brown, about 10 minutes. If bottom is soft, bake 3 to 5 minutes more.
5. Remove tart from oven, and arrange soft cheese over top. Using an offset spatula, slide tart onto a wire rack; let cool slightly. Cut into pieces; serve warm or at room temperature (tart can stand at room temperature up to 1 hour).