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1
Cut hot dogs lengthwise 3/4 of the way through.
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2
Insert a piece of cheese or 1/2 teaspoon caramelized onions into each hot dog, if using; set aside.
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3
If not using cheese or onions, poke hot dogs several times with the tip of a knife.
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4
On a lightly floured work surface, working with one sheet of puff pastry at a time, roll into a 14-by-11-inch rectangle.
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5
Cut lengthwise into seven 1 1/2-inch wide strips.
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6
Cut each strip crosswise into 4 rectangles, each about 3 1/2 inches long.
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7
In a small bowl, beat together egg and 1 tablespoon water; set aside.
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8
Line baking sheets with parchment paper or a nonstick baking mat; set aside.
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9
Place a hot dog on the narrow end of one piece of pastry.
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10
Roll to enclose, brushing with some of the beaten egg to adhere; transfer to prepared baking sheet.
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11
Repeat process with remaining hot dogs and pastry.
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12
Brush the tops of puff pastry with egg and sprinkle with seeds, if using.
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13
Transfer to refrigerator and let chill for 15 minutes.
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14
Preheat oven to 450 degrees.
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15
Transfer baking sheets to oven and bake until puffed and golden, about 20 minutes.
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16
Let cool briefly before serving with mustard and ketchup.
