Make dough: Combine milk and water in a microwave-safe bowl; cook in the microwave for 10-second intervals until warm to the touch or an instant-read thermometer reads 100 degrees F (38 degrees C). Stir in sugar and yeast; let sit for 15 to 20 minutes.
Stir together flour and kosher salt in a large bowl; make a well in the center. Pour yeast mixture and melted butter into the well; stir with a fork until a shaggy dough forms, 1 to 2 minutes. Switch to your hand and knead in the bowl until a ball of dough is formed. Transfer dough to a work surface and knead until very smooth, soft, and elastic, 7 to 8 minutes.
Transfer dough to a lightly greased bowl; cover and let rise in a warm spot until doubled in size, about 1 hour.
Preheat the oven to 400 degrees F (200 degrees C). Adjust the oven rack to the center position. Line a baking sheet with a silicone mat.
Make topping: Stir together rice flour, sugar, salt, vegetable oil, sesame oil, yeast, and warm water in a small bowl. Add more water if needed to form a thick but spreadable mixture. This must be thin enough to spread over rolls without deflating them but thick enough not to run off onto the pan. Cover the bowl with plastic wrap and set aside until needed.
Transfer risen dough to a work surface and press out air while rolling into a short, fat tube shape. Divide evenly into 6 pieces.
Shape each piece into a ball by pulling and pinching dough at the bottom to form a smooth skin over the top surface of dough ball. Transfer to the prepared baking sheet. Cover with a clean, dry tea towel and let rise until doubled in size, about 30 minutes.
Uncover rolls and use a small spoon to carefully spread topping over each one.
Bake in the center of the preheated oven until rolls are golden brown and the tops have cracked, about 20 minutes. Transfer to a wire rack and allow to cool to room temperature before serving.