To make the raspberry sauce, add the raspberries, lemon juice, and sugar to a medium sauce pan.
Heat over medium heat, stirring frequently to break up the raspberries, until the mixture comes to a simmer.
In a small bowl, whisk together the corn starch and water.
Pour the corn starch mixture into the pot, stir to combine, and cook 2-3 minutes, until thickened.
Remove from heat and let cool completely.
To make the lemonade, in a small saucepan over medium-high heat, combine sugar and one cup of water.
Bring mixture to a boil, stirring often until sugar is completely dissolved (about 5 minutes).
Allow mixture to come to room temperature and chill for 1 hour.
In a large pitcher, combine juice from lemons, the remaining seven cups of water and the sugar water mixture.
Stir well and chill.
To assemble, spoon two tablespoons of raspberry sauce into the bottom of a glass.
Add ice and pour lemonade to fill the glass. Stir and enjoy.