Tonkatsu sauce

1. Measure the ketchup and Worcestershire sauce into a small bowl.

2. Add the soy sauce, sugar and mustard.

3. Stir with a spoon until the sugar has completely dissolved and the sauce is glossy and smooth.

4. Taste: if it's too sharp add a pinch of sugar, if too sweet a drop of Worcestershire sauce.

5. Leave for at least 10 minutes so the flavours blend.

6. Serve with tonkatsu, korokke, fried fish and katsu sando; it keeps for 2 weeks in a sealed jar in the fridge.

Tip: Tonkatsu sauce is the thick, fruity-spicy brown sauce of Japanese fried dishes. If you like, stir in a little grated apple or a drop of honey – that brings it even closer to the original.