Place the water and kombu in a small pot or saucepan, and bring to a boil. Let it simmer for 15 minutes. As the kombu broth is simmering, put 2-3 tablespoons of cold water into a small bowl, and sprinkle gelatine powder over it, leaving it to bloom/hydrate for at least 5 minutes. When the broth has finished simmering, add in the bonito flakes, sugar, and mirin. Let simmer for another 5 minutes, then strain out the solids. Add the bloomed gelatine into the dashi broth, bring it to a boil then remove from the heat. Let the broth cool down for 10-15 minutes, then pour it into a deep tray or container. Keep in the refrigerator overnight to allow jelly to set.
Rice
Rinse the sushi rice 2-3 times to remove the excess starch, then add the water and piece of kombu to the rice. Cook this in a rice cooker as per the rice cooker’s instructions (or cook it in a pot for 15 minutes over medium heat).
Rice seasoning
In a small saucepan, combine the vinegar, sugar, and salt. Heat it up and stir until the sugar and salt dissolves, then take it off the heat and let it cool down. (Alternatively, you can heat and dissolve the sugar and salt in a microwave.) Pour this seasoning over the cooked rice, and stir gently to incorporate it into the rice, careful not to break up the individual rice grains.
Scrambled eggs
Combine the eggs, cream, and salt in a saucepan, and place over low heat. Keep stirring the pot with a spatula or whisk. At first it’ll seem like nothing is happening, but after 1-2 minutes, the egg will start to set on the bottom. Keep stirring and scraping up the curds as it forms on the bottom of the pan until the scrambled eggs has lost most of its liquid, but is still thick, shiny and malleable. This should take 5-7 minutes. Taste the eggs at the end and season it to taste if need.
Serve
Place the rice into a bowl, and flip it over onto a plate so it’s shaped like a dome. Spoon the scrambled eggs over the rice, and using the back of the spoon (or a spatula), gently push and ease the egg around so that it covers the rice. Then, cut up the dashi jelly into little cubes and place all around the egg-rice-dome. Garnish with some salted kombu, sesame seeds, and scallion slices.