Preheat oven to 400*F, wrap beetroot in foil and roast in middle of oven until tender, 1 1/2 to 2 hours.
Unwrap beet and cool.
Peel the beet with the help of a paper towel and grate on the large side of the grater.
Into a bowl add the grated beet, diced sweet onion, mayonnaise and season with salt and sugar. (also add garlic if desired)
Mix everything to combine and serve.