Line a 9-inch square pan with aluminum foil and oil it or spray with nonstick cooking spray. Set aside.
In a medium saucepan, combine granulated sugar, 1 ½ cups of water, and lemon juice. Stir over medium heat until the sugar dissolves. Bring the mixture to a boil.
Brush down the sides of the pan with a wet pastry brush to prevent sugar crystals from forming. Insert a candy thermometer.
Allow the sugar mixture to continue boiling, without stirring, until it reaches 240℉, this can take from 35 - 60 minutes.
When the sugar syrup is around 225℉, begin the starch mixture.In a slightly larger saucepan, add the remaining 3 cups of water, cornstarch and cream of tartar and whisk until the cornstarch is completely dissolved with no lumps.
Bring the mixture to a boil, whisking constantly to avoid lumps. Remove from heat when mixture is thick and pasty.
When the sugar syrup is at 240 slowly and carefully pour it into the cornstarch mixture while whisking to avoid cornstarch lumps.
Simmer mixture over low heat, whisking every 8 to 10 minutes until it is light yellow and very thick and gluey, about an hour.
Remove the pan from the heat, stir in the rose water and food coloring (if using). You can mix in the nuts here (if using) or wait until the next step
Pour the candy into the prepared pan and allow it to sit uncovered on the counter for 6-8 hours.If you want the nuts suspended in the middle of the candies, pour half of the candy into the pan, sprinkle with nuts then top with the remaining candy mixture.
When the candy has set dust a clean work surface with powdered sugar. Remove the candy from the pan using the foil to lift it out. Flip it onto the powdered sugar. Remove the foil.
Using a sharp knife dipped in oil, cut into small squares (about 1 inch). Cover the pieces with the remaining powdered sugar, making sure all sides are coated.Store in an airtight container for about 1 week.