Pour 10 cups of water into a pot and bring it to a boil. In a bowl, combine the starch, sugar, and the remaining 2 cups of water. Mix well, then add the mixture to the boiling water. Stir continuously and, when the water boils again, reduce the heat to medium. Continue to stir occasionally and cook for 20 minutes. Add the rose water and ice cubes, stirring until the ice cubes melt. Pour half of the mixture into a 23x30cm pan. Add the rose syrup to the remaining mixture, mix well, and pour the pink mixture into a second 23x30cm pan. Let both types of mahalepi cool for 2-3 hours, then refrigerate to set. If storing for more than one day, pour 1 cup of water on top to prevent a skin from forming.
For Serving: To make cutting easier, pour ice-cold water over the top. Place the cut mahalepi pieces in a bowl and add extra rose syrup. This dish is a perfect, refreshing choice for family gatherings and parties.