01 - Add coarsely ground coffee and cold filtered water to a large jar or pitcher. Stir well, cover, and refrigerate for at least 12 hours or overnight to steep.
02 - After steeping, strain the coffee through a fine mesh sieve or coffee filter into a clean container to separate the grounds.
03 - Fill two tall glasses with ice cubes.
04 - Pour 1 tablespoon of hazelnut syrup into each glass.
05 - Divide the strained cold brew concentrate evenly between the glasses, filling each about three-quarters full.
06 - Top with milk or non-dairy milk if desired, and stir gently to combine. Optional: Garnish with whipped cream and chopped toasted hazelnuts before serving.