Hazelnut syrup is typically made by combining natural or artificial hazelnut flavoring with sugar or a sweetener, water, and sometimes additional ingredients such as preservatives or stabilizers. The flavoring used in hazelnut syrup can be derived from real hazelnuts or created synthetically to replicate the taste. The specific ingredients and ratios may vary depending on the brand and recipe used to make the syrup. It's important to read the label or product information to understand the exact composition of a particular hazelnut syrup.