Place the onion, garlic, ginger, turmeric and chili powder into a food processor and process until a paste is formed.
Heat the oil in a deep-sided frying pan, carefully add the spicy paste (at this stage it will splutter), stir it into the oil, lower the heat and cook gently for about 10 minutes. If the mixture starts to burn, add a little water.
When the paste is cooked it should be a golden brown color and have oil around the edges.
When well cooked and sizzling, add cumin and coriander.
Then add meat and fry, stirring for a few minutes.
Add salt, about 4 cups water and simmer slowly for 15 minutes.
Add potatoes and simer until meat is tender and potatoes are cooked.
Note : Some cooks prefer to rub the cumin, coriander and salt into the beef before cooking.