Position an oven rack in the center of the oven and preheat to 375 degrees F. Turn a large baking sheet over, then cut a piece of parchment large enough to cover the bottom of the baking sheet.
Lightly dust a work surface with flour. Stack 2 crescent dough sheets on top of each other, then use a rolling pin to roll the dough into a rectangle slightly larger than the parchment, about 17 inches by 13 inches. Gently transfer the dough to the parchment on the inverted baking sheet. Repeat with the remaining dough sheets, setting the second rectangle aside on the work surface. Brush the dough on the baking sheet with the beaten egg, sprinkle with half the poppy and sesame seeds and top with the cheese, leaving a 1/2-inch border all the way around. Top with the reserved rectangle of dough and pinch the sides to close.
Position a 3 1/2-inch bowl upside down in the center of the dough. Use a sharp knife to make 1 cut from the center of the top edge of the dough rectangle straight down to the rim of the bowl, 1 cut from the center of the bottom edge of the dough rectangle straight up to the rim of the bowl, 1 cut from the center of the left edge of the dough rectangle straight to the rim of the bowl and 1 cut from the center of the right edge of the dough rectangle to the rim of the bowl, dividing the dough into 4 equal pieces. Make 2 additional cuts within each piece so that you have 12 pieces total (some will be larger than others, but try your best to make the pieces as even as possible). Remove the bowl from the center.
Put 1 hot dog on each piece of dough so the ends meet in the middle of the dough. Gently wrap the piece of dough around each hot dog. Space the wrapped hot dogs as evenly apart as possible. Brush the dough all over with the beaten egg and sprinkle with the remaining poppy and sesame seeds.
Bake, rotating the baking sheet halfway through the cooking time, until the dough is puffed and golden brown, about 30 minutes. Transfer to a large cutting board. Fill a small bowl with spicy mustard and put into the baked dough in the center. Serve immediately.
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