Heat 1 tbsp oil and add the butternut squash. Stir-fry over medium-high heat for about 10 minutes or until the squash starts to soften.
Add sugar and cashew cream, stir well, and continue to cook, stirring, for about 30-35 minutes or until all of the liquid has disappeared and the halwa is thick and gooey.
Stir in the cardamom powder and take off heat.
In a small saucepan or skillet, heat the remaining 1 tsp oil
Add cashews or raisins if using, and stir-fry for a couple of minutes until the raisins puff up and the cashews are lightly golden.
Pour over the halwa and mix.
Serve at room temperature or cold.