Evenly mix ground beef with soy sauce and corn starch. Set aside.
In a food processor (you can do this by hand of course), pulse ginger and garlic until finely minced. Divide 1/3 of the amount in a bowl, 2/3 of it in a small sauce pot. Then pulse the onion until finely chopped as well. Set aside. In the sauce pot with 2/3 of the minced garlic and ginger, add 1/2 cup of oil and set on medium heat. Fry the ginger and garlic until golden brown. Stir constantly to prevent sticking and burning. This has to happen slowly otherwise the edges would get burnt before it turns crispy, approx 7~10 min. The second it turns golden brown (one minute longer they will burn and become bitter), drain them through a fine sieve and leave on a paper towel. Reserve the oil.
In a wok or skillet, heat up 4 tbsp of the ginger/garlic oil on high heat. Saute the chopped onion until the edges are browned. Add the ground beef and saute until nicely browned as well. The browning of the onion and beef is IMPORTANT in developing a deep rich flavor so take your time. Now add the 1/3 of the minced ginger, garlic and curry powder, and saute until fragrant. Add the cooked rice at this point. With 2 spatulas, press and turn the rice so that every grain is separated and coated in oil and curry powder. Microwave the Japanese curry bricks in a bowl until melted, approx 1 minute on high. Add the melted curry to the rice along with the coco powder, dashi granule and black pepper. Turn and flip with 2 spatulas until every rice is evenly coated.
To serve, add the crispy garlic and ginger on top. Add 1 egg yolk in the middle and a nub of unsalted butter to melt.