Tartare sauce is the very thing for fish and is brilliant made fresh. The name goes back to Genghis Kahn who was the leader of the Tartar hordes. Though I am not sure they had a sauce quite like this.
4 egg yolks
1/2 level tsp English mustard
Pinch of salt and pepper
330 ml clear oil
Peeled and chopped garlic clove
10 g fresh parsley chopped
25 g washed and finely chopped capers
4 chopped baby gherkins
Juice of a lemon
Make the mayo first by mixing the yolks, lemon juice salt and pepper and mustard into a food processor and whizz.
Slowly add the oil a drizzle at a time until all is incorporated.
Then remove the mayo from the food processor and spoon in and mix the rest of the ingredients.
The key is to get all the chopped ingredients as fine as possible.
Keep cool and use within five days.