Use a knife to poke the potatoes, you should poke them about 8 to 10 times all around.
Place the potatoes on an oven tray lined with baking paper. Bake for 60–70 minutes or until the potatoes are soft.
Cut the potatoes in half and let the steam escape for 5 minutes.
Use a spoon to scoop out the inside of the potatoes. Use a kitchen cloth if they are too warm to hold.
Push the peeled potatoes through a sieve using the back of a spoon. Scrape the bottom of the sieve as well. If you have a potato ricer, use it instead or mash the potatoes with a fork. Let the mashed potatoes cool completely.
Add to a bowl the following ingredients: flour, a beaten egg, parmesan cheese, salt and pepper. Mix with a fork until all combined. Then, knead by hand until all ingredients are well incorporated.
Lightly flour the kitchen counter. Cut the dough into smaller pieces and roll each piece into a thin rope.
Cut the dough into small chunks. Roll the chunks into small balls, use flour to prevent sticking. Press each ball gently against the inside of a fork, then roll the edge up and fold the edges together. Place the gnocchi on a chopping board. Repeat until all the dough is used.
Bring a pot of water to a boil and add salt.
Heat a frying pan over medium-high heat. Add butter and let it melt.
Meanwhile, cook the gnocchi for about 90 seconds, or until they start floating.
Reserve some pasta water using a cup or ladle. Add the pasta water to the melted butter in the pan. Be careful, as it might splatter.
Tear and bruise the sage, then add it to the frying pan. Add extra Parmesan and pepper. Stir until the cheese has melted and you have a thin silky sauce.
Use a slotted spoon to add the gnocchi to the frying pan. Combine all ingredients.