1. Pour 5 cups of water into a pot. Place it on the heat to boil. Pour the remaining water, 1 cup, into a bowl and add the cornstarch. Stir with a whisk until the cornstarch dissolves. Once the water boils, slowly pour in the cornstarch mixture and stir with the whisk.
2. Lower the heat and let the mahalebi simmer for 20 minutes. The longer it simmers, the firmer and whiter the mahalebi will be. Stir occasionally. Don't worry, it won't stick. Lightly wet 6 shallow dishes with a little water, then pour out the excess. Pour the mahalebi into them. Let it cool, then pour a little water over the top to cover it. This will help prevent a skin from forming on the mahalebi. Place it in the refrigerator to chill and set, for about 3-4 hours. If desired, once set, you can transfer the mahalebi 'discs' into a bowl and cover them with water to save space in the fridge. Serve the mahalebi with extra water, and let everyone add as much rose-flavored syrup, rosewater, and sugar as they desire.
3. To make the rose ice cubes, pour ¼ of a glass of rose syrup and fill the rest with water, almost to the top. Pour the rose mixture into an ice cube tray and place it in the freezer to set. Once the ice cubes are ready, serve them with the mahalebi.
