1) Put the rapeseed oil and coconut oil in a saucepan over a medium heat.
2) Add the mustard seeds and fry until they start popping.
3) Add the onions and fry for 5 minutes until they are soft stirring regularly.
4) Stir in the garlic and the rest of the spices and fry for a few minutes.
5) Crumble in the stock cube then add the tinned tomatoes and salt and pepper to taste.
6) Add enough water to fully cover the onions, bring to a simmer then cover and cook for 20 minutes.
7) Use a stick blender to blitz the sauce until it is smooth.
Add vegetables, meat or fish to the sauce at the point the tomatoes are added and adjust the cooking time accordingly.