For the best flavor, toast the pecans in a dry skillet over medium heat for a few minutes, or until fragrant. The crepe batter can be made ahead of time and stored in the refrigerator for up to 24 hours. Whisk well before using. If you don't have hazelnut syrup, try using a different flavored syrup, such as almond or caramel, or simply omit it for a more classic flavor. Serve the crepes immediately for the best texture, or store them in the refrigerator for up to 2 days.