3 medium sweet potatoes, peeled and coarsely grated (about 4 cups/600 g)
1 small red onion, finely chopped
2 garlic cloves, crushed
1-inch (2.5 cm) piece fresh ginger root, peeled and finely grated
2 tablespoons brown rice flour
2 tablespoons cornstarch
2 red chiles, 1 finely chopped and 1 finely sliced
Sea salt and freshly ground black pepper
Large handful of cilantro leaves, roughly chopped
¼ cup plus 2 tablespoons (90 ml) olive oil or coconut butter, melted
2 ripe avocados, halved and pitted
2 limes, 1 juiced and 1 quartered
Using a colander held under a cool tap, rinse the grated sweet potatoes until the water runs mostly clear. Squeeze the rinsed gratings in a clean kitchen towel to remove excess water, then transfer them into a large mixing bowl.
Add the onion, garlic, ginger, rice flour, cornstarch, the chopped chile, salt and pepper to taste, about 1 tablespoon of the cilantro and 2 tablespoons of the oil, and mix everything well.
Divide the remaining oil between 1 1/2 × 6-inch (4 × 15 cm) cast-iron or heavy-bottomed frying pans—or a 9-inch (23 cm) pan to make a large cake—and place over high heat. Add one quarter of the potato mixture to each pan, or all of it to the large pan (it should sizzle loudly) and flatten firmly with a spatula. Reduce the heat to medium.
Cook each cake for 3 to 5 minutes (perhaps slightly longer for the larger version), then run a palette knife or spatula around the edge, transfer each cake out on to a flat plate, then slide back into its pan the other way up. (Don’t attempt to flip these unless you’re a black belt.) Return to the heat for about 3 minutes more until the underside is nicely browned.
Scoop the avocados out of their skins with a spoon and mash roughly with a little lime juice, the remaining cilantro, sliced chile and seasoning to taste. Serve each hot sweet potato cake with the avocado mixture spooned on top and lime quarters to squeeze over.