Pour the chilled cola into a mixing bowl and stir in the granulated sugar and vanilla extract until fully dissolved, creating a sweetened cola base.
Transfer the sweetened cola mixture into a shallow baking dish or lined tray to facilitate quick and even freezing.
Place the dish in the freezer and let it chill for about 2 hours, stirring every 30 minutes to prevent large ice crystals from forming and to promote a smooth, slushy texture.
Once the mixture is mostly frozen but still scoopable, break it into chunks and transfer them into the blender jar.
Blend the frozen cola mixture on high speed for 30-60 seconds until it reaches a smooth, velvety consistency similar to a thick slush.
Pour the blended slushie into chilled glasses, allowing the icy, caramel-colored treat to settle and mound slightly at the top.
Serve immediately with a straw or spoon for an icy, flavorful dessert that melts in your mouth, revealing rich cola flavors.
