Preheat the oven to 200°C fan (220°C conventional). Line a baking tray with parchment paper.

Leaving the skin on, cut the sweet potatoes into 170g pieces. Halve the eggplants lengthways, brush with oil, and place cut side down on the tray with the sweet potatoes.

Roast until both eggplants and potatoes are soft and well browned on the bottom, about 45–50 minutes. Remove from the oven, cut the potatoes into pieces, and set aside to cool.

While the potatoes are cooling, scoop out the eggplant flesh (discard the skins) and place in a bowl with basil, olive oil, butter, cumin, coriander, tomato puree, canned tomatoes, salt, pepper, and nutmeg. Mash together with a fork.

Scoop the sweet potato flesh into another bowl (discard the skin) and mash. You should have about 300g of mash. Add egg yolk, masa harina, salt, pepper, and nutmeg, and mix until just combined.

On a floured tray lined with parchment, roll the dough into long ropes and cut into gnocchi pieces. Dust lightly with masa harina.

Bring a large pot of salted water to the boil. Drop the gnocchi in in batches; when they float to the surface, cook for 30 seconds more before removing with a slotted spoon. Transfer to an oiled tray.

To serve, warm the ragout in a saucepan, then toss through the gnocchi. Finish with parmesan, extra basil leaves, lemon zest, pepper, nutmeg, and a drizzle of olive oil.