Boil the egg hard, quench, peel, finely chop. Peel the onion, quarter the cucumber lengthways and cut out the seeds lengthways along with the watery inner workings. Now finely chop the onion, cucumber, anchovy fillet and half the caper apple. Please do not take capers.
Now mix all the ingredients well with the mayonnaise, then stir in the sour cream to the desired consistency and finally season with salt, pepper and sugar. Let the tartar sauce soak in the refrigerator for at least 24 hours.
It can be kept refrigerated for up to 14 days in an airtight container.