Heat the oil in a slow cooker using the sauté/sear function, or in a pan over a medium-high heat. When the oil begins to shimmer, stir in the onions and fry for 5 minutes or until soft and translucent.
Add the garlic and ginger paste, stir it into the onions and fry for a further minute. Stir in the curry powder or mixed powder and chilli powder, then add the passata, stock or water, sugar, tamarind concentrate and chutney and bring it all to a simmer.
At this point you can leave the sauce as it is or blend it using a stick or countertop blender for a smoother sauce.
Add the sauce to the slow cooker, cover with the lid and cook the sauce on the high setting for 2 hours or low for about 4 hours. Stir in the prawns and let them cook into the sauce for the last hour of cooking, keeping an eye on them to ensure they don’t overcook – they are ready when white all the way through and no longer at all transparent or raw-looking.
When the prawns are cooked through, add the kasoori methi by rubbing it between your fingers over the sauce. Add lemon juice and salt to taste and garnish with the chopped coriander to serve.
For the curry powder
Roast all the whole spices, including the dried chillies, if using, in a dry frying pan over a medium-high heat until warm to the touch and fragrant but not smoking. Move the spices around in the pan so they roast evenly, and be careful not to burn them or they will become bitter.
Tip the warm spices on to a plate and leave to cool, then grind to a fine powder in a spice grinder or pestle and mortar. Add the turmeric, chilli powder, if using, garlic and onion powders and stir to combine. Store in an airtight container in a cool, dark place for up to two months.
Recipes and photographs taken from Curry Guy Slow Cooker by Dan Toombs, photography by Kris Kirkham
