Tamarind is ace. It imparts a deep, rich and sweet flavour to curries. Buy a block and put it in your fridge, it keeps for months, and you can hack a piece off and chuck it in your curry just like that. That's what I did in this lovely chana (chickpea) curry.
Note that the block sort-of dissolves as it cooks, and leaves behind inedible pips. If you prefer not to spit out pips then you could put the tamarind in a paper teabag perhaps, so you can fish it out afterwards.
You can change the veg choices in here - the red pepper is a nice bright contrasting flavour - but in particular the baby aubergines do this great thing of going gooey and helping to create the sauce. Full-sized aubergines don't seem to do that, in my experience. It's the tamarind and the aubergine that go to add body to the sauce, I think - I don't add any tomato or anything like that, and yet the sauce is flavoursome and thickened.
Heat the oil in a largeish deep pan which has a lid, on quite a hot frying heat. Add the spice seeds and the cloves - you might like to put the lid half-on at this point because as the seeds fry and pop they'll jump around and may jump out at you.
After 30 secs or so with the seeds, add the onion, then the chilli and the powdered spices. Give it a good stir round. Let the onion fry for a minute or two before adding the red pepper and the aubergines. Fry this all for another couple of minutes, stirring occasionally.
Add the chickpeas, the beetroot with its juices, the tamarind block, and maybe 1 cup of boiling water (don't add too much water - not enough to cover the mixture). Give this a good stir, then put the lid on, turn the heat down to its lowest, and let it bubble for 30 minutes or so. It can be longer or shorter, I'd say 20 minutes is an absolute minimum. No need to stir now, you can go and do something else, as long as you're sure it's not going to bubble over!
When the curry is nearly ready, take the lid off, turn the heat up to thicken the liquid if needed, and give it all a stir.
Give it a good twist of black pepper, then serve it up in bowls, with coriander leaf sprinkled on top. Serve it with bread (eg naan or roti).