Pour 2 to 3 inches of oil into a large, deep-sided skillet and heat over medium to 350 degrees F.

Thread a hotdog piece lengthwise onto an 8-inch wooden skewer. Follow with a mozzarella piece so they meet each other, with the tip of the mozzarella flush with the tip of the skewer. Repeat with the remaining hot dogs and mozzarella pieces, making 6 total skewers.

For the dredge: In a shallow bowl, add ½ cup all-purpose flour. Combine the remaining ¾ cup all-purpose flour, the rice flour, sugar, salt and baking powder in a mixing bowl and whisk to combine. Then add the seltzer and beaten egg and whisk to make a thick batter. Transfer the batter to a tall thin glass or jar. In another shallow bowl, add the panko.

Once the oil has reached temperature, dredge the hot dogs by first dipping the assembled skewer in flour to lightly coat all over. Shake off any excess, then dip all the way into the batter until coated completely. Place the battered hot dog in the panko and sprinkle with the crumbs, gently pressing them into the batter until the hot dog is fully coated. Repeat the dredging process with 2 more of the prepared skewers.

Carefully add the skewers to the hot oil and fry, turning once, until crispy and golden brown all over, 3 to 4 minutes total. Remove to a wire rack to drain of excess oil. Sprinkle with salt while still hot, followed by a touch of sugar. Repeat with the 3 remaining skewers. Serve with ketchup and mustard.

Korean corn dogs are best eaten as soon as they are made, but leftovers will keep, wrapped in foil in the fridge, for a day or two, and should be rewarmed in a toaster oven.