Dahl is one of those things you see in an Indian restaurant as a side order and never quite get around to ordering. But it's easy to make (in a pan as well as a slow cooker) so it's a useful vegetarian dish for week nights. Here's how I made mine:
250g / 1 1/4 cups red lentils - no need to soak
1 onion (I used red), finely chopped
2 tins (400g / 14 oz) chopped tomatos
2 tbsp curry paste of the hotness you require. I used Patak's Biryani which is tomato/coriander
1 pint / 500 ml water
fresh coriander leaf/ cilantro to add at the end
Dump and go. Cook it on low for 8-10 hours.
This ended up as a nice, spicy vegetarian lentil stew but it didn't taste like I expect dahl to taste. I won't cook it this way again. I think it's better made with yellow split peas (if you live in Cambridge, try the incomparable Al-Amin stores on Mill Road for these) and I'd rather come up with my own spice blend next time rather than use the curry paste. Maybe a different spice paste would have done the trick.