1Place half of the raspberries in a blender container or food processor bowl.
2Cover and blend or process until berries are smooth.
3Press berries through a fine mesh sieve; discard seeds.
4Repeat with remaining berries.
5You should have about 1 cup sieved puree.
6Stir together sugar and cornstarch in a medium saucepan.
7Add sieved berries.
8Cook and stir over medium heat until thickend and bubbly.
9Cook and stir for 2 minutes more.
10Remove from heat.
11Cool slightly, then cover and chill.
12Makes about 1 cup sauce.