Lay both pairs of Fanta cans flat in the freezer for at least 6 hours, ideally overnight. My first attempt sat for only 2 hours, and the slush turned to blue soup within a minute of pouring. Frozen solid cans blend into fine, even crystals; half-frozen cans turn to mush instead of snow.

Break both frozen cherry cans into rough chunks with a butter knife, then drop them into the blender. Add 2 cups crushed ice, half the corn syrup, and the citric acid, then blend in three short pulses. The mix is ready when it looks like packed wet snow. A spoon should stand straight up in it.

Pour the cherry slush into two tall glasses. Tip each glass onto its side in the freezer, propped against the wall. Freeze for 15 minutes so the layer sets on a slant. A glass that slides back to flat won’t hold the angled line, so wedge a folded towel behind it.

Repeat the same blending process with both frozen Fanta Berry cans. Use the rest of the crushed ice, corn syrup, and blue gel coloring. The blue mix should look just as thick as the cherry batch, not runnier.

Pull the angled glasses from the freezer and set them upright. Pour the blue slush slowly over the back of a spoon held against the glass wall. A steady hand keeps the seam sharp. A fast pour blurs the two colors into purple.

Drop a drained maraschino cherry on top, add a straw, and serve within 5 minutes. The layers start bleeding together fast once the glass sits at room temperature. A glass that sits out too long turns the sharp line into a solid purple blend within 10 minutes. Snap a photo before the first sip, since the layers won’t last.

Blend a second full batch of each flavor. Freeze it flat in a shallow pan for a fast refill later. This backup batch keeps its scoopable texture for about 3 days in the freezer.