Preheat the oven to 375 degrees F. Mix together the poppy seeds, garlic, onion and sesame seeds in a small bowl; set aside.
Whisk together the flour, sugar, baking powder, baking soda and 3/4 teaspoon salt in a medium bowl. Add the butter and work it into the flour mixture with your fingers until the butter is broken down into very small pea-size pieces. Make a well in the center and pour in the milk. Using a fork, stir the dry ingredients into the wet.
Once the dough comes together, knead it gently a couple of times on a well-floured surface. Roll out the dough to a little thinner than 1/8 inch. Cut as many 1 1/2-by-3-inch rectangles as you can. (You should get at least 30 pieces.) Place a mini hot dog onto each rectangle and roll it up, making sure the short ends overlap; seal and arrange seam-side down 2-inches apart on a baking sheet. Brush each dough-wrapped hot dog with the egg and top with 2 generous pinches of the topping.
Bake in the oven until golden brown, 17 to 20 minutes. Serve with mustard on the side, for dipping.
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