Read the bottle before measuring; jam, fruit puree and a concentrated baking flavor are not equivalent to the listed blackberry drink syrup. Divide syrup and vanilla between both glasses, then add ice before the soda. Use the glass size as a starting minimum and leave enough space for the cream finish and carrying.
Drizzle the cold cream into each drink and stir gently for the violet swirls. Brand acidity and sweetness vary, and the recipe warns that cream may separate as the glasses stand. Serve promptly rather than trying to fix a waiting drink with repeated stirring or extra unmeasured cream. Keep the cream cold until this final step and make the next round separately when needed.
Timing and servings are estimates. Equipment, ingredients and portion sizes affect the result.
