Combine cashews, yogurt, tomato paste, vinegar, garam masala, coriander, ginger, red pepper, and garlic in a blender or food processor.

Process until smooth to create a marinade.

Combine the marinade and chicken pieces in a large bowl.

Cover the bowl and refrigerate for at least 3 hours, or preferably overnight, to marinate.

Heat a large Dutch oven over medium-low heat.

Coat the pan with cooking spray.

Add chopped onion, crushed green cardamom pods, and a cinnamon stick to the pan.

Cover and cook for 10 minutes, or until the onion is golden, stirring often to prevent burning.

Add the marinated chicken mixture to the pan.

Cook for 10 minutes, stirring frequently, until the chicken starts to brown.

Stir in chicken broth, tomato puree, sweet paprika, and salt.

Scrape the pan to loosen any browned bits stuck to the bottom.

Cook for 1 hour, or until the sauce has thickened, simmering gently.

Stir in half-and-half to add richness to the sauce.

Cook for 1 minute more, stirring occasionally, until well combined.

Remove the Dutch oven from the heat.

Discard the cinnamon stick.

Garnish with chopped fresh cilantro, if desired, before serving.