In a saucepan, combine sugar with part of the water and lemon juice. Heat gently, stirring until sugar dissolves, then bring to a boil.
Keep the syrup at a steady boil while you whisk cornstarch with the remaining water until smooth.
Stir the cornstarch mixture into the hot syrup while stirring. Continue cooking, stirring often, until thick, glossy, and heavy.
Stir in vanilla extract, rose water, and red food coloring (optional).
Pour into a parchment-lined dish and smooth the top. Let set until firm.
Mix powdered sugar and cornstarch for the coating.
Turn out, cut into cubes, and coat all sides generously.
