Prepare a clean stainless-steel worktable by lightly dampening it with cold water. Have rigid plastic bowl scrapers and an airtight storage container ready.

Combine the granulated sugar, glucose syrup, and water in a saucepan. Stir while heating until the mixture comes to a boil and the sugar has dissolved.

Stop stirring and continue cooking until the syrup reaches 243°F (117°C). Keep stray sugar crystals from accumulating on the sides of the saucepan.

Carefully pour the syrup onto the prepared worktable, leaving any crusted material behind in the saucepan. Lightly sprinkle the surface of the syrup with cold water to prevent a dry crust from forming. Let it cool undisturbed to 120°F (50°C).

If using prepared fondant as seed, place it on the cooled syrup immediately before beginning agitation.

Work the syrup continuously with the scrapers. It will become opaque, creamy, and eventually form a firm, short-textured mass. Allow approximately 8 minutes with seed or 20 minutes without seed. Judge completion by texture rather than the clock.

Pack the finished fondant into an airtight, food-safe container and leave it to ripen overnight at a cool room temperature. Do not refrigerate.