In a medium saucepan, whisk together the flour and 1 cup of the cold water until you form a smooth, lump-free paste (this is the "slurry").
Add the remaining 1 cup of water, sugar, and salt to the pan; whisk thoroughly to combine.
Place the saucepan over medium heat, stirring constantly with a wooden spoon or whisk.
Continue stirring until the mixture begins to bubble and thickens to the consistency of a thin pudding or smooth custard.
Once thickened, remove the pan from the heat immediately and allow the glue to cool completely to room temperature.
Transfer the cooled glue to a glass jar or airtight plastic container for storage.
