In a frying pan on medium heat, toast cashews until golden brown and crisp. Set aside and allow to cool completely.
In a heavy-bottomed saucepot, add jaggery and water and bring to a boil. Stir to ensure jaggery is dissolved, and continue to cook until thickened.
To test the texture of the jaggery when set, drop a small blob into a bowl of cold water. If it sinks to the bottom and becomes crisp, it is ready. If it dissolves in the water, it must be cooked longer.
Remove from heat, and quickly stir in ginger followed by the cashews, ensuring the nuts get evenly coated.
Pour nut mixture onto greased baking tray and spread out as evenly as possible. Place a piece of waxed paper over top of mixture, and using a rolling pin, gently roll out until approximately a centimeter thick.
Remove wax paper, and score the brittle into squares while warm. This will make it easier to cut the brittle when it has set.
Cut into pieces and enjoy! Store in an airtight container to maintain crispness.