In a shaker or blender, add the instant coffee and sugar.
Pour in a small amount of cold water, just enough to cover the coffee and sugar.
Shake or blend vigorously for about 10-15 seconds until the mixture becomes frothy and creamy. The shaking process is essential for creating the signature foam (kaimaki) of the frappé.
Fill a tall glass with ice cubes.
Pour the frothy coffee mixture over the ice cubes, including the foam.
Add cold water to the glass, leaving some space for milk if desired.
Stir gently to mix the coffee, water, and foam together.
If desired, add a splash of milk to taste. This step is optional and can be adjusted based on personal preference.
Serve immediately and enjoy your refreshing Greek frappé!