1. Wrap in foil ½ kg of potatoes with the skin, olive oil and salt. Put it in preheated oven for about 30-40 minutes or until it is well-cooked.
2. Peel the potatoes and mixed with peas puree. Let it cool down and add 1 cup of flour without baking powder, salt, pepper and a beaten egg.
3. Mix gently until you get a homogeneous dought that´s stick in the hands. Let it rest for 30 minutes.
4. Stretch the dough and shape it into ½-inch diameter cylinder; now cut 1/3-inch pieces and bury with a fork. These lines will allow the sauce to spread better in the dough.
5. Cook them with salty boiling water; when the gnocchi floats, they´re cooked.
6. For the sauce: in a small pot on a low heat melt the butter and add the sage, salt, pepper and a pinch of nutmeg. Stir slowly with a wooden spoon and simmer for 15 minutes. Don´t stop stirring, It´s very important the low heat so it doesn´t burn.
7. If you want to, you can add a peeled garlic clove when you take the pot out of the fire, it´ll give some extra flavor to the sauce.