Add the frozen raspberries, blue raspberry syrup, and crushed ice into the blender.
1 cup frozen raspberries, 1/2 cup blue raspberry syrup, 1 cup crushed ice
Blend on high speed until the mixture is uniformly slushy and smooth, with a frosty texture and no large ice chunks.
Stop the blender and check the consistency; if it's too thick, add a splash of water and blend briefly to loosen it up.
Pour the icy blue raspberry mixture into tall glasses, filling them just to the rim.
Garnish with fresh raspberries or a sprig of mint for a colorful finishing touch.
Serve immediately with a straw, and enjoy the bright, icy burst of berry flavor.