Rinse the parsley thoroughly, pluck the leaves and dry them in a salad spinner or a tea towel. Place the parsley leaves and garlic in a blender with 100 ml of the oil and blend for a couple of minutes, until the oil is green and has a smooth consistency. If you want the mayonnaise to be completely smooth, pass the oil through a fine-mesh sieve. Now mix the parsley oil with the rest of the oil.
Place the egg yolks in a large bowl together with the mustard, a little salt, pepper and 1 tbsp vinegar, and whisk well with an electric whisk, or if you have a good balloon whisk to make the mayonnaise. Now whisk the oil into the egg yolks a little at a time in a thin stream. Pour slowly enough that the oil is constantly being whisked into the egg yolks. Pause occasionally whilst adding the oil and whisk the mayonnaise thoroughly. Continue until all the oil has been added, then whisk in a little water. Whisk thoroughly again – this helps ensure the mayonnaise doesn’t separate and gives it a nice, smooth consistency. Finally, season to taste with salt and, if desired, extra lemon juice.
Herb mayonnaise tastes best if it is slightly on the tangy side, and if you make it with parsley, season it with a little freshly grated garlic.
Refrigerate the mayonnaise immediately, where it will keep for 5–6 days.
Peel and boil the potatoes until tender. Drain the water and leave them to cool slightly. Press the potatoes through a potato ricer or mash them through a sieve into a bowl. Add the butter to the bowl of warm mashed potatoes and mix well. Allow to cool slightly, then stir in the egg yolks. Finely chop the chives and garlic and stir into the mash. Season with grated nutmeg, salt and pepper.
Place the mixture in a disposable piping bag and cut a hole in the bottom, about the size of a cork. Place a sheet of baking paper on a tray that can go in the freezer. Pipe long strips of the mixture onto the baking paper and place in the freezer until the mixture is completely firm. Cut the strips into smaller pieces the size of a cork. Gently coat them first in flour, then in beaten egg white and finally in breadcrumbs.
Heat oil in a pan to 180 degrees; the oil is ready when it sizzles around a wooden skewer. Fry the croquettes a few at a time until golden. Drain them on a piece of kitchen roll and serve immediately with the parsley mayonnaise.
