Measure out the fresh raspberries and place them in your blender.
1 cup fresh raspberries
Add the whiskey, simple syrup, and freshly squeezed lime juice to the blender with the raspberries.
1/4 cup whiskey, 2 tablespoons simple syrup, 1 lime lime juice
Pour in the ice cubes, filling the blender until it’s nearly full.
2 cups ice cubes
Secure the lid on the blender and blend on high until the mixture is perfectly smooth and frosty, about 30 seconds.
Stop the blender and check the texture—if it’s too thick, add a splash of water or more lime juice and blend again briefly.
Pour the slushie into glasses, garnish with a few fresh raspberries or a lime wedge if desired.