Add a single tablespoon of finely ground sugar to your mixing bowl, along with two tablespoons of freshly squeezed lemon or yuzu juice.
Measure out roughly two tablespoons of rice vinegar, then add to the mixture, followed by a half teaspoon of Japanese mustard. Sprinkle a pinch of salt over the mixture, then mix well using a wooden or metal spoon to combine the flavors. Continue stirring thoroughly until the sugar and salt have been fully absorbed into the liquid.
Pour the egg yolks into the food processor, followed by the contents of the glass mixing bowl. Blend the two together at full speed for 20-30 seconds, or until the egg yolks have fully liquidized.
Switch on the processor again, and whilst the contents are blending, gradually add 250ml of Canola oil. It is best to add the oil a little at a time, as this allows it to be gradually incorporated into the mixture.
Repeat this process for the warm Dashi stock, adding it gradually to the mixture until the correct consistency is achieved. Kewpie mayonnaise is characteristically thinner and creamier in texture than Western commercial varieties, so, if the mixture is still too thick, you can add additional Dashi stock to achieve a thinner consistency.
Note: If you intend to use Kewpie mayo primarily for decoration or piping onto sushi rolls, you may want to limit the amount of Dashi stock used in Step 3.