Chop the onion finely, saute with the ground meat, and season with salt and pepper. When it's cooked, turn off the heat and swirl in the ☆ katakuriko dissolved in water. Mix in well to heat through.
Cut each hanpen into 4 small triangles. Make a cut into the bottom of each triangle to make little pouches.
Stuff the cooled meat mixture into each hanpen triangle pouch. It's about 2 tablespoons each. Be careful not to rip the hanpen, and stuff them very full. This way, the hanpen won't shrink when they're deep fried and will look nice.
Dissolve the flour in the water. Dip the stuffed hanpen triangles in the batter, then coat with panko. Do this part carefully since the filling tends to fall out.
Deep fry the triangles in 360F/180C. Hold each triangle with your fingers, filling side down, in the oil for a few seconds. This is to make a lid. Even if they're not coated properly, the filling won't drop out.
After a few seconds, release the triangle and deep fry as usual. The filling is already cooked through so you just need to fry them until they're golden brown on the outside.
Story Behind this Recipe
My mother used to make this for me a lot when I was little. Her version was big and crumbly and kind of hard to eat, but I loved it. I added katakuriko dissolved in water to the batter, and made them easier to eat.
If you push in a lot of filling with a spoon, the stuffed triangles will be soft, fluffy, and crispy. If you're afraid of holding the triangles in the oil in Step 5, just put the stuffed triangles in the oil. If the breading is stuck properly to the surface the filling won't come out.