Heat the oil in a pan over a low heat then add the cumin and fennel seeds. Cook for 30 seconds, stirring.
Add the remaining ingredients and 200 ml water. Mix everything together in the pan. Cook over a low heat for 10-12 minutes until the dates are soft and the tamarind looks really dark and sticky.
Remove from the heat and leave to cool. Once cool, transfer to a sterilised jar with a lid and keep in the fridge.