Steps

1. Confirm that the 1 piece of pork loin (for tonkatsu) is about 1cm thick.
   🕒 00:31
2. Heat vegetable oil to approximately 160℃. 【Here's the trick!】 Drop a small amount of the coating into the oil; it's ready when it hits the bottom and immediately rises. It's best to fry the cutlet in plenty of oil so it's half submerged.
   🕒 00:57
3. Fry the 1 piece of pork loin in oil at 160℃. 【Here's the trick!】 Don't cook it all the way through; remove it from the heat when it's about 80% cooked and let the residual heat finish cooking it. Over-frying will cause the cutlet to become dry when served in katsudon.
   🕒 03:25
4. In a bowl, mix [A] 2 tbsp soy sauce, [A] 2 tbsp mirin, [A] 1 tbsp sake, [A] 6 tbsp water, [A] 2g granulated dashi stock, and [A] 3g sugar to make the katsudon sauce. 【Here's the trick!】 A 4:1 ratio of soy sauce to water creates a well-balanced flavor.
   🕒 04:27
5. Slice the 1/4 onion.
   🕒 06:36
6. Add the prepared katsudon sauce and the sliced 1/4 onion to a frying pan and simmer until the onion is softened. 【Here's the trick!】 The sauce should be about half its original volume when the onion is tender.
   🕒 06:36
7. Once the sauce has reduced, cut the fried 1 piece of pork loin cutlet into appropriate sizes and place it in the pan.
   🕒 07:46
8. Pour the beaten 1 egg over the cutlet, cover, and steam until the egg is cooked to your desired consistency. 【Here's the trick!】 Mixing the egg well so no clear parts remain makes for a better presentation. Soft-cooked is recommended.
   🕒 07:56
9. Serve 1 bowl of rice in a donburi bowl, then top with the egg-coated cutlet. 【Here's the trick!】 If you prefer it sweeter, serve as is. If you prefer it saltier, add more soy sauce to adjust.
   🕒 09:35