Fry the eggplant and potatoes separately in a wok with oil until the vegetables are browned. Drain the fat on kitchen paper and set the vegetables aside.
Put the caraway and mustard seeds in the pan, which is not too hot, and stir until you smell the smell (it works relatively quickly). Add the onion, garlic and ginger to the pan. When the onions are translucent, add chillies and curry paste. Stir again until you can feel the smell.
Put the potatoes in the pan and simmer with the tomatoes and water until cooked. Finally add the eggplant, spinach and sugar and simmer until the spinach has collapsed.
Serves well with rice or pasta, but bread does too.