Add the wine, Grand Marnier, frozen strawberries, frozen blackberries, frozen raspberries and simple syrup to a blender.
Blend until smooth.
Strain the mixture through a fine-meshed sieve into a freezer-safe container. *If you don’t mind the seeds from the berries being in your slushie feel free to skip this step.
Freeze for at least 3 hours or overnight.
Remove the mixture from the freezer and use an ice cream scoop to scoop the slushie into individual glasses. Alternatively, you can use a fork to scrape and breakup the slushie before serving.
Top with frozen berries if desired.
