Add sesame seeds to a medium pan and toast them until aromatic (~3 minutes). Make sure to toss them frequently to avoid them getting burnt. Allow to cool down for a few minutes.
Add toasted sesame seeds to a mortar and pestle (or food processor / coffee grinder) and grind until you have a fine powder.
Add the fine, ground sesame powder into a mixing bowl or a salad jar, and add Japanese mayonnaise, rice vinegar, soy sauce and toasted sesame oil and sugar. Whisk well and serve!