For the Korma Paste:

1. Begin by heating the vegetable oil in a frying pan over medium heat. Add the cumin seeds, coriander seeds, and cardamom seeds. Gently fry these spices, stirring occasionally, until their aromas are released and the air is filled with their fragrant scent. This usually takes a few minutes.
2. Once the spices are fragrant, remove the pan from the heat and allow the spices to cool down.
3. In a food processor, combine the cooled spice mix with the garlic, ginger, tomato puree, green chillies, cashew nuts, coriander sprigs, desiccated coconut, garam masala, and ground turmeric.
4. Process these ingredients to form a relatively smooth paste. Depending on the consistency, you may need to add a small splash of water to assist the blending process.
5. Once the paste is ready, it can be used in your favorite dishes just like a store-bought korma curry paste.

For the Chicken Korma:

1. Heat 1 tbsp of the vegetable oil in a large frying pan over high heat. Sear the chopped chicken in batches until each piece is golden brown. Avoid crowding the pan to ensure even cooking. Once seared, remove the chicken from the pan and set aside.
2. Reduce the heat to medium and add the remaining 1 tbsp of oil to the pan. Gently fry the chopped onion until it becomes soft and translucent. If the onions start to stick, add a little more oil.
3. Stir in the korma curry paste with the softened onions. Let it fry for about 3 minutes, stirring occasionally. This process will help release the flavors and aromas of the spices in the paste.
4. Return the seared chicken and its juices to the pan, mixing it well with the onion and paste mixture. Then, stir in the Greek yogurt, ensuring the chicken is well coated.
5. Allow the mixture to simmer gently over low heat for about 10 minutes. This slow cooking helps the chicken absorb the flavors.
6. After 10 minutes, add the double cream and brown sugar to the pan. Stir well to combine all the ingredients.
7. Continue to simmer the korma for an additional 5 minutes. During this time, the sauce should thicken slightly and the chicken will be cooked through.
8. Taste the sauce and add salt as needed to suit your preference.
9. Serve the chicken korma immediately, ideally with rice, naan bread, or your choice of accompaniment.