Heat oil in a moderate sized saucepan and add onion, cook for one minute until soft and add Madras curry paste and cook for a further minute stirring frequently.
Add chicken pieces, stir and coat in the paste mixture then add tomatoes and coconut milk & salt.
Simmer, covered for 45 minutes, stirring occasionally.
Siphon off enough curry liquid to use for the dipping sauce, ensuring there is enough left for the reduction of the main curry and continue simmering for 15 minutes.
Sautéed Cabbage:
Sauté the cabbage in butter for 3-4 minutes in a medium hot saucepan. Add salt to taste.