Combine elderflower syrup and chopped strawberries in a medium saucepan. Bring to a boil over medium heat and cook for a few minutes, until strawberries are tender.
Strain mixture to a jar and cool to room temperature. Instead of discarding the strawberries, store them covered in the fridge and serve over ice cream.
To serve: divide syrup between 4 large glasses (about 500ml / 1 pint in volume), add 2-3 big scoops of ice cream to each, pour over mineral water until it reaches the edge of the glass. Add a straw to each drink and enjoy!
If your grocery store doesn’t stock elderflower syrup, you can also get it on Amazonor at Ikea.