Put the fly knife in the bowl, pluck the parsley from the stems and finely chop the parsley, remove. Finely chop the chives. Peel and quarter the onion, coarsely chop the cucumber, place in the appliance bowl and chop medium-fine (about 1/2 minute on the highest setting).
Add the remaining ingredients except for the oil and stir briefly (about 1 minute on the lowest setting).
Then gradually drip the oil through the funnel directly into the running knife until you have a creamy tartar sauce. Season to taste with salt and pepper.