Put the sweet potatoes in a baking tray and bake until you can easily push a skewer through it. Let it cool then scoop out the flesh. This can be done days ahead - just keep the flesh chilled.
Finely chop the onion and mince the garlic.
Heat a spoonful of oil in a pan and gently sauté the onion until soft and slightly caramelised. Add the garlic and herbs, then stir for a minute or so, until fragrant. Let it cool.
Mash the beans in a large bowl until you get a textured mash. Add the sweet potato flesh, the onion mixture and rice flour. Combine well.
Add the corn and chopped herbs of your choice, mix well again, then form 6-8 balls. Flatten them between your palms, then put them on a plate and chill for 30 minutes or until you’re ready to cook.
Heat some oil in pan or turn your grill on. Put some rice flour in a bowl and coat the patties, then fry them in the hot oil 2-3 minutes on both sides until golden. If grilling, spray them with some oil and put them on a baking sheet or directly on a rack. Grill for 3-5 minutes on each side.
Serve warm in a bun or flat bread with side dishes and condiments of your choice.