Roast 2 tbsp toasted white sesame seeds in a dry frying pan on a medium-high heat for a few minutes until fragrant.

Grind the roasted sesame seeds with a mortar and pestle.

Transfer the ground sesame to a bowl and add 2 tsp Japanese soy sauce (koikuchi shoyu), 2 tsp Worcestershire sauce, 1 tbsp tomato ketchup, 1 tsp sugar and 4 tsp water. Mix until well incorporated and set aside for later.