15 large green pimento stuffed olives, about 1 1/4 inches long
1 medium egg yolk
1 tablespoon milk
On a lightly floured work surface, roll out puff pastry to a 12 1/2-by-6-inch rectangle, about 1/8-inch thick. Using a large sharp knife, cut the rectangle into a 5 1/2-by-6-inch rectangle and a 7-by-6-inch rectangle. Place both rectangles on a baking sheet and transfer to refrigerator; let chill 20 minutes.
Place the 5 1/2-by-6-inch rectangle on a baking sheet. Place 5 olives, end-to-end, in a straight line along the short side of the rectangle, leaving about a 5/8-inch border. Repeat process two more times to make three lines of olives.
In a small bowl, whisk together egg yolk and milk. Brush egg mixture on all exposed spaces between olives. Cover with the 7-by-6-inch rectangle of puff pastry, pressing the whole surface of the dough between the olives firmly with your fingertips. Transfer to refrigerator; let chill 20 minutes.
Preheat oven to 425 degrees. Using a very sharp knife, trim edges of dough; cut crosswise into 1/4-inch-wide straws. Lay flat-side down on a baking sheet. Transfer to oven and bake until pastry is golden and crisp, 5 to 6 minutes. Transfer straws to a wire rack to cool slightly. Serve warm.