Preheat and Prepare: First, preheat your oven to 220°C (200°C fan). Line two large baking trays with baking parchment. Using two trays is important to avoid overcrowding the fries, which would cause them to steam rather than roast.

Cut the Potatoes: Wash and scrub the sweet potatoes well. There's no need to peel them. Trim the ends, then cut each potato into fries that are about 1cm thick. Try to keep them as uniform as possible.

Soak the Fries: Place the cut fries into a large bowl and cover them completely with cold water. Let them soak for at least 30 minutes, or up to an hour. This step removes excess starch and is crucial for getting a crispy finish.

Dry Thoroughly: Drain the water from the fries and pat them completely dry with a clean tea towel or paper towels. This is a vital step – any remaining moisture will prevent them from crisping up in the oven. I usually spread them on a towel and pat them down firmly.

Coat with Oil: Place the dry fries back into the (now dry) large bowl. Drizzle with the 2 tablespoons of olive oil and toss well until every fry is lightly coated.

Add the Seasoning Mix: In a small bowl, whisk together the cornflour, smoked paprika, garlic powder, onion powder, cayenne pepper (if using), fine sea salt, and black pepper. Sprinkle this mixture over the oiled fries and toss again until they are evenly coated.

Arrange on Trays: Spread the seasoned fries in a single layer across the two prepared baking trays. Make sure they have plenty of space and are not touching. This is key for allowing hot air to circulate and create a crispy exterior.

Bake to Perfection: Bake for 15-20 minutes, then carefully remove the trays from the oven and use tongs or a spatula to flip the fries over. Return to the oven and bake for another 10-15 minutes, or until they are golden brown and crisp at the edges.

Serve Immediately: For the best texture, serve the sweet potato fries straight from the oven. Sprinkle generously with flaky sea salt just before serving.