Leave room for the foam
Measure the syrup into both glasses first, then divide the ice cream. Add the chilled soda slowly and pause whenever foam approaches the rim. The stated glass capacity leaves room for that reaction; filling a smaller glass with the same measured ingredients is likely to make pouring harder. A spoon belongs beside each serving before you begin.
Keep the drained cherries ready for the final step, with the remaining ice cream back in frozen storage. Assemble only the two drinks you will serve immediately. If making another round, measure it afresh rather than pouring soda into glasses that have been waiting with melted ice cream. The layered effect is most useful when the drink reaches the table promptly.
