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1
Combine the dashi, soy sauce, mirin, and sugar in a jug and stir until the sugar dissolves. Set aside. The broth is ready when the sugar is fully dissolved and the liquid is uniform.
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2
Heat the oil in a heavy pot over medium-high heat. Add the sliced meat in a single layer and stir-fry briefly until it just changes colour — no longer pink. This is the Maillard foundation on which the dish's depth rests. The meat is ready when the raw colour has gone and the surface is lightly seared.
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3
Add the onion wedges to the pot and cook, moving them once or twice, for 2 minutes, until softened at the edges and fragrant. Add the potato chunks and turn them briefly in the fat to coat.
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4
Pour the combined broth over the ingredients in one motion. Do not stir. Place an otoshibuta (drop lid) directly on the surface of the liquid — or cut a circle of baking parchment to fit — and bring to a gentle simmer. This is where the dish lives or dies: once simmering begins, the pot must not be stirred; any agitation will break the potato apart and produce a dissolving mass rather than intact, broth-glazed pieces. Simmer uncovered under the drop lid for 20 minutes. The potato is ready when a skewer meets moderate resistance — almost tender but still just holding its shape.
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5
Add the rinsed shirataki to the pot, again without stirring. Replace the drop lid and simmer for a further 5 minutes. The noodles are ready when they have absorbed the remaining broth and are translucent throughout — they should be the most intensely flavoured element in the pot.
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6
Remove the pot from the heat and leave to rest, covered, for 10 minutes. During this period the residual heat continues flavour penetration into the potato and noodles. The dish is ready when each ingredient is dressed in a reduced, glossy sweet-soy glaze rather than sitting in a pool of liquid — nikujaga is not a soup.