For the fondant, first of all, it is best to take a fireproof shallow mold, spread it very thinly with oil and put it in the refrigerator.
While it is cooling, melt sugar with water. Boil the syrup to a small ball (dip a cooking spoon in the sugar, then in cold water: the sugar must be elastic, but no longer viscous). Lift off impurities that settle.
Pour into the cold bowl and let cool a little. Then work the quantity well with a spatula so that the sugar becomes white and firm. Always work from the outside in until you have a smooth, just kneadable mass.
Store the fondant wrapped in plastic wrap in a dry place until use.