Heat ½ cup water in a small saucepan.
Add the butterfly pea flowers and let them steep for 5-10 minutes, or until the color is vibrant.
Strain out the flowers and return the infused water to the pan.
Stir in ½ to 1 cup of sugar, depending on the concentration you prefer—standard simple syrup (1:1) or rich syrup (2:1). Once the sugar has completely dissolved, remove from heat and allow to cool slightly. a (If the water has cooled too much, reheat gently.)
Add in the elderflower flavour drops and stir well.
Transfer the syrup to a clean, airtight container and refrigerate until thoroughly chilled.