Wash and drain the radish leaves.
Heat oil in a pan. Chop the onion and saute it in the pan until it starts to soften. Stir in curry powder and heat for a minute.
Chop the radish leaves, stirring down periodically, in a food processor until finely ground. (You may need to do this in two batches).
Add the chopped leaves to the pan, and stir over medium heat until it begins to cook. It will probably exude liquid - let that start to simmer.
Lower the heat and cook, stirring periodically, for 20 minutes.
Taste for seasoning. If you add more curry powder, stir it in and heat another minute or two before removing pan from heat.
Serve at once, or refrigerate or freeze for later.