Roast cashews on low to medium heat until heated through, about 5 minutes. Make sure to not brown them as it will change the taste. Note: You can also air fry cashews at 300 F for 3 minutes without preheating the air fryer.
Add water, sugar, and saffron to a medium pan and bring it to a boil. Once the syrup starts bubbling, check for the one string consistency (see notes).
Add the cashews and cardamom. Turn the heat off. Add rose petals and pistachios if using. Mix well. Keep stirring as the sugar syrup thickens and coats the cashews. The sugar syrup will completely dry out after 5 to 7 minutes.
Take out the cashews in a tray. Separate any that are sticking to each other. Allow the cashews to completely cool. Store in an airtight container.
Notes
How to check for one-string consistencyMethod 1: Add a few drops of syrup to a small plate and allow it to cool for a few seconds. Then dip your index finger in the syrup and press it on your thumb. Slowly open and close the index and thumb fingers and you should see a string being formed between the two fingers. For best results remember to allow the syrup to cool just a bit before you test it.Method 2: Use a digital thermometer and dip it in the syrup. For accuracy, make sure that the thermometer tip is not touching the bottom of the pan. Once the thermometer reaches 220 F which should be around 4 to 5 minutes turn the heat off.