In a heavy-bottomed pan, heat butter and oil over medium heat. Add cardamom, cloves, and bay leaf; toast lightly until fragrant.
Stir in ginger-garlic paste and cook for 5-7 minutes, or until the raw aroma fades.
Add green tomatoes, cashews, green chilies, coriander stems, and salt. Sauté until the tomatoes become translucent.
Add a splash of water, cover with a lid, and simmer for 20 minutes, or until the tomatoes and cashews have softened.
Remove from heat and let cool. Discard the bay leaf.
Blend the mixture into a smooth puree, adding water as needed for a sauce-like consistency.
In a clean pan, heat a teaspoon of butter. Add the blended korma sauce and finish with cream. Adjust seasoning to taste.