Cut the chicken into bite sized cubes. In a small bowl combine the rest of the marinade ingredients. Add the chicken and marinade to a large bowl. Cover and refrigerate for at least one hour up to overnight.
In a large skillet, heat the olive oil. Add the chicken in batches and brown all sides. You don't have to cook the chicken all the way through at this stage. Remove the chicken and set aside.
In the same pan, add the butter. Once the butter is melted, add the onion. When the onion starts to sweat add the tomato paste, spices, jalapeno, and cinnamon stick. Cook until onions are soft and translucent. Add the tomatoes and cashews. Cook for a few more minutes until everything is bubbling.
Remove the cinnamon stick and add heavy cream. Spoon the sauce into a blender and blend until smooth. Add the sauce back to the pan. For a smoother sauce, pass it through a fine mesh sieve.
Bring the sauce to a simmer over medium heat. Add the chicken back in and simmer for 20 minutes. Add salt and pepper to taste.
Top with cilantro and serve with naan bread and basmati rice.