Soak the hazelnuts in filtered water overnight: Place nuts in a bowl, submerge in filtered water. Cover and leave on your countertop overnight.
Rinse the soaked nuts. In a high-speed blender, add the hazelnuts and filtered water.
Leave unsweetened or add sweetener and flavouring of choice.
Blend on high for a few minutes.
Strain out the pulp: In a large bowl, open the nut milk bag. Gently pour in the hazelnut milk. Close the bag and squeeze out the milk with clean hands.