Cut the sweet potato in half, leaving the skin on and blanching in boiling water for 5 minutes. Allow this to cool.
While the potato cools, get on with prepping the rest of your veg. Cut the tomatoes in half and place these cut side down in a heated frying or griddle pan along with 2 spring onions and the ear of corn. Allow these to cook until they char, rotating the corn and spring onions to ensure all sides colour evenly. You only want to char the cut side of the tomato. When this is nicely charred remove from the pan and set aside on a plate to cool.
Once the sweet potato is cool enough to handle, grate it into a cloth over a bowl and let it sit, allowing the cloth absorb any additional moisture.
Next, finely slice and the remaining spring onions and add this along with a bit of oil, cumin and coriander seeds, and red chilli until fragrant, this should take 3-4 minutes.
Squeeze any remaining liquid out of the sweet potato using the cloth and add the potato to a bowl along with the onion, spices, and rice flour along with a good pinch of sea salt and black pepper. Mix until well combined. Heat the oven to 180C(fan)/160C(non-fan)/gas mark 4.
Next heat a bit of oil large frying pan (need dimensions), enough to coat the bottom of the pan. Press the rosti mixture into an even layer in the pan. Allow this to cook for 3-4 minutes on a medium heat on both sides.
Whilst your rosti cooks, add your beans to a small sauce pan along with half the chopped dried chilli, smoked salt and a glug of olive oil to heat through.When your rosti is ready, turn it out onto a large baking tray and pop it on a tray and in the oven for 5-10 minutes to further crisp while you make the salsa.
Make your salsa by adding the tomatoes (chopped into eighths), corn cut from the cob and chopped spring onions into a bowl with the lime juice, the remaining ancho chilli, olive oil, coriander and a pinch of salt & pepper. Stir to mix.
Serve the rosti on a plate or wooden board, topped with the beans and salsa.