Over the years, I have developed a recipe that is effectively aloo gobi and saag aloo mixed together: Potato, cauliflower, broccoli and spinach curry. (I used to make it with sweet potato, but to "please" all my diners, I've switched to regular potatoes...which is also more authentic.)
Anyway, the curry gravy is fried black mustard seeds, browned-off onions, ground fenugreek, ground turmeric, hot chilli powder, ground coriander, diced ginger, red chillies, dried curry leaves and chopped tomatoes. The vegetables are roasted and added to the gravy after it's stewed for a while (20-40 minutes, say). Then I mix through the spinach at the end.
When I first started making this, I remember it tasting better than it does now. It always tastes bland, nowadays. If there's any spice, it's mostly from the ginger; even if I minimise its quantity (or remove it altogether) and focus instead on the fenugreek and chilli. I roast the vegetables specifically for the Malliard reaction and to sweeten them up, but it doesn't help much. Often, the overwhelming flavour is the tomato, but the gravy dries out and burns if you don't use enough.
It's quite frustrating and, because there are so many variables, I'm not sure where I'm going wrong. I have tried adding more spice; it doesn't really make a difference. I have tried leaving the gravy to "infuse" for longer; that helps to a point, but with diminishing returns. My spices are just supermarket spices -- nothing fancy -- but relatively new, so shouldn't have lost their potency. Should I toast them first? Salting the vegetables doesn't make any difference. Some recipes I've seen post-fry the vegetables to crisp them up, but I don't see how that can work with a gravy-based curry.
What's the secret to a good vegetable-based curry?