Line a 9 x 9 inch pan with aluminum and spray with cooking spray. Set aside.

Medium saucepan, combine the sugar, 1 ½ cups of water, and lemon juice. Bring to a boil, whisking frequently. Use a wet pastry brush to prevent sugar crystals from forming on the saucepan. Once the mixture comes to a boil, insert a candy thermometer, and allow it to continue to boil, without stirring, until it reaches 240°F.

While the mixture is boiling, combine the cornstarch, cream of tartar, and the remaining 3 cups of water in another larger saucepan. Stir with a whisk to remove any lumps. Place the saucepan over medium heat and bring to a boil. It will become very thick.

When the sugar mixture has reached 240°F, slowly pour into the cornstarch mixture, whisking continuously. Return to a boil and continue to cook for about an hour, stirring occasionally to prevent it from burning. The mixture will become very thick and turn a pale yellow color. After an hour, remove from heat and add the rosewater.

Pour the candy into the prepared pan and allow to set in a cool place (but not the refrigerator), uncovered, overnight.

 remove from the pan to a surface sprinkled with powdered sugar. Cut with a greased knife and roll in the shredded coconut. If the candy is particularly sticky, roll in more powered sugar.