Heat the oven to 200 C / 390 F. Pierce each sweet potato 4 to 5 times with a fork, place directly on the oven rack, and roast for 45 to 55 minutes until completely soft when pressed.

Cut the sweet potatoes in half and scoop the flesh onto a large baking sheet. Spread it out and let it sit for 5 minutes to release steam. You need 400 g of dry, cooled flesh.

Pass the sweet potato flesh through a potato ricer or fine-mesh sieve into a large mixing bowl. This step removes lumps and keeps the dough smooth.

Add the beaten egg, salt, nutmeg, and Parmesan (if using) to the sweet potato. Mix gently with a fork.

Add 130 g of rice flour and the tapioca starch. Mix until a soft dough forms. If it sticks to your hands, add more rice flour 1 tablespoon at a time, up to 160 g total. The dough should be soft but not tacky.

Do not over-knead. Mix only until the flour is just incorporated and the dough holds together.

Lightly dust a clean work surface with rice flour. Divide the dough into 4 equal pieces.

Roll each piece into a rope about 2 cm thick. Use a bench scraper to cut each rope into 2 cm pieces.

Optional: press each piece gently against the tines of a fork and roll slightly to create ridges. This helps sauce cling to the gnocchi.

Place shaped gnocchi on a parchment-lined sheet pan in a single layer. Do not stack them.

Bring a large pot of salted water to a gentle boil (about 1 tsp salt per liter of water). Drop gnocchi in batches of 15 to 20 pieces. Do not crowd the pot.

Cook until the gnocchi float to the surface, then give them another 30 to 45 seconds. Remove with a slotted spoon and transfer to a plate.

Melt butter in a wide nonstick skillet over medium heat. Swirl the pan as the butter foams. When it turns amber and smells nutty, add the sage leaves. They will crisp in about 30 seconds.

Add the cooked gnocchi to the pan in a single layer. Cook for 1 to 2 minutes without moving them, until lightly golden on one side.

Flip gently, cook 1 minute more, then remove from heat. Finish with a pinch of flaky salt and shaved Parmesan if desired. Serve immediately.