This mashed celeriac with parsley is not only delicious and very versatile, it retains a brilliant green color that always looks great on the plate.
It is an excellent complement to practically any fish or meat, and goes particularly well with calf's liver. It has also become part of my Thanksgiving menu because it is so perfect with turkey, mushrooms, and cranberry sauce.
Bring two large pots of water to a boil with each 2 Tbsps of coarse sea salt.
Peel the celeriac and the potatoes and cut them into large chunks.
Place each vegetable in a different pot of boiling water and cook until soft. The time this takes depends on the size of the pieces of vegetable and how crowded they are in the boiling water, but I usually start checking by poking it with a sharp knife after about 10 minutes. It is ready when the knife goes in with no resistance. *It's important to cook the celeriac and potatoes separately because they don't take the same amount of time to cook through and it's important not to overcook the potatoes; if they start falling apart the consistency of the mash will be watery.*
Wash the parsley and trim off the stems.
In a blender, purée the parsley with the olive oil and 1 tablespoon of water.
Once the roots are cooked, mash them with a potato masher or through a food mill (never in a food processor).
Mix in the butter, a good slosh of good olive oil, and season with salt, pepper, and freshly grated nutmeg. (If the mash needs to be reheated, do it before you add the parsley, otherwise it will turn brown and loose its vibrant taste.)
Just before serving, add the parsley purée to the mash and stir well until it is uniformly green.
Taste and adjust seasoning one last time if necessary.