To make the horseradish sauce, whip the cream to stiff peaks. Stir together the crème fraiche, horseradish, chives, mustard and lemon juice. Season with salt and pepper. Fold in the whipped cream and refrigerate while waiting for the roast to finish cooking.
Peel the celery root and potato and grate on the large hole side of a box grater. Mix with the egg, parsley and enough matzo meal to hold the mixture together. Season with salt and pepper.
Heat a wide bottom skillet over high heat. Add enough vegetable oil to the pan to be about a ¼ inch deep. Place a large spoonful of the celery root mixture in the pan and flatten slightly with the back of the spoon. Repeat several more times without crowding the pan too much. One latkes are brown on one side, flip with a metal spatula. Cook until brown and crisp and remove from the pan to a resting rack set over a sheet pan. Repeat with the remaining celery root mixture. Add more vegetable oil as necessary. Serve with a spoonful of the horseradish sauce and the optional dab of your favorite caviar!
Enjoy with a glass of Cakebread Cellars Cuttings Wharf Chardonnay.