Add 1 tbsp oyster sauce, 1 tbsp Japanese soy sauce (koikuchi shoyu), ½ tbsp Worcestershire sauce, 1 tsp tomato ketchup, ½ tbsp sake, ½ tsp sugar, 1 pinch ground black pepper¼ tsp curry powder, and 1 tsp toasted sesame oil to a small bowl and mix thoroughly.
Feel free to adjust ingredient quantities to suit your preference. Use to stir fry with noodles, vegetables and meat. You can see the full yakisobe recipe here.
Notes
Adjust ingredient ratios to suit your taste: for example, more soy sauce makes it thinner and saltier; more ketchup makes it sweeter and thicker.
Cook this sauce together with noodles, meat, and vegetables; avoid using it cold/uncooked.
I like this rich modern yakisoba flavor, but for a more traditional flavor, reduce oyster sauce and soy sauce ratios while increasing Worcestershire sauce ratio.
Use curry powder only as a secret ingredient for depth and subtle spice (maximum ¼ teaspoon) It's not meant to create a curry flavor.