1. Place the peanuts in a food processor and process briefly until coarsely ground. Alternatively, grind them in a mortar with a pestle. Transfer to a bowl and stir in the sweetcorn, onion, flour, coriander and sambal ulek. Season to taste with salt. Knead to a dough, adding a little warm water, if necessary, to make the dough workable.
2. Heat the oil in a deep-fryer or large heavy-based saucepan. Using your hands, form tbsp of the dough into balls, then drop the sweetcorn balls into the hot oil, in batches, and cook until golden and crisp.
3. Remove the sweetcorn balls with a slotted spoon, drain on kitchen paper and keep warm while you cook the remaining batches. Serve immediately or leave to cool first.