This recipe comes from Jason French, chef and owner of Ned Ludd in Portland.
Make a loose mayonnaise with the egg yolks, lemon juice and oil. Start by whipping the egg yolks and half the lemon juice until light in color and creamy in texture. Season with salt and start adding the oil a few drops at a time, whisking constantly. Once an emulsion is achieved you can add the oil more quickly. Adjust the texture with lemon and salt. If the mayonnaise is still too thick a small amount of cold water may be added.
Fold in the remaining ingredients and allow to sit covered in the refrigerator for a few hours for the flavors to meld.
Dress the celery root and apple with enough remoulade to coat. Plate and cover with chopped, roasted hazelnuts.