Prick the sweet potatoes with a fork and roast them whole in the pre-heated oven at 200°C (390°F) for 30-40 minutes. Oven time varies depending on sweet potato size. They are done when tender enough to easily pierce with a fork. Let cool until cold enough so that you can handle them with your hands. This step takes about 1 hour, you can make it ahead and store the roasted sweet potatoes wrapped in clingfilm in the fridge up to 5 days.
Make the sweet potato gnocchi
Peel and mash the roasted sweet potatoes. Add to a bowl together with the flour, starch and egg. Knead until a homogeneous dough comes together.
Take 1/4 of the dough and roll it into a sausage shape as thick as 2 fingers. Using a knife or bench scraper, cut the dough sausage slightly on the diagonal every 1 cm. Repeat until you have cut up all of the dough. Keep the dough lumps on a floured surface making sure they don't touch each other or they may stick together.
To give dough lumps a traditional gnocchi shape roll each lump up into a ball. Gently press each and every dough ball against a textured surface (like a gnocchi board or the back of a fork) with your thumb, impressing little ridges on the side.
Cook the gnocchi
Bring a large pot of water to a boil. Gnocchi need to be cooked in batches to avoid overcrowding the pot. Salt the water and add one part of the gnocchi to the boiling water. Cook for a couple of minutes, until they come to the surface. Simmer for one more minute then remove the cooked gnocchi with a skimmer. Add the next batch of gnocchi and repeat. How many batches will depend on the size of your pot.
Make the brown butter and serve
Add the butter to a saucepan and set on medium heat. When the butter has completely melted, simmer for about 5 minutes, stirring occasionally. The evaporation of the water in the butter will cause the protein (white particles) to separate from the fat (yellow liquid). Keep simmering the butter until the white particles turn light brown. If it's frothy, move the froth with a rubber spatula in order to be able to see inside the pan. Remove from the heat as soon as the particles have browned and transfer into a bowl to stop the cooking process and prevent the proteins from burning.
Pour the browned butter over the cooked gnocchi and toss to distribute the condiment all over. Add a handful of fresh sage leaves and bring it to the table. Your roasted sweet potato gnocchi are ready to be served!
Notes
Gnocchi may get hard and chewy with time so it is recommended to consume them on the same day as they were made. However, you can save some preparation time by roasting the sweet potatoes ahead of time.The nutritional information provided is made by an online calculator and is meant to only be used as an estimate.