Tried this tonight for my wife as she is veggie. I cut back somewhat on the spices and garlic as they seemed a bit too much, and it turned out fanstastic! I think adding the garlic tarka makes this dish. For the veg, I used pre-cooked potato and carrot, and also added some mushroom during the cooking. I can honestly say that it was better than virtually any rogon joshes I've had at restaurants or takeaways. And the wife agreed.
Only slight difference I made was that for the oil, I used only 3/4 veg oil, then 1/4 hot curry oil from Asda, plus 1 tsp of ghee. I used this methoid for a chicken korma a few days ago (only 1 tsp of curry oil though), and this turned out very, very good too. Maybe the curry oil adds something a little different to the cooking, I don't know. Anyway, really chuffed!! ;D