Bring 6 quarts water to boil and add 2 tablespoons salt.
In a mixing bowl, crush potatoes with a masher until smooth. Add cheese, chives, eggs and nutmeg and mix well.
Roll out pasta to thinnest setting and cut into 4-inch squares. Place 1 tablespoon potato mixture in center of each square. Fold opposite corners of each square together and press firmly to seal and form a triangle. Bring the opposite points of the triangle together and press firmly to meld. Continue until all pasta is stuffed and formed into tortelli. Drop pasta into boiling water and cook until tender, about 6 to 7 minutes.
Meanwhile, melt butter in a 12 to 14-inch saute pan and continue cooking until golden brown color (noisette) appears in the thinnest liquid of the butter. Add sage leaves and remove from heat. Add lemon juice and set aside. Drain tortelli well, gently pour into saute pan and return to heat. Add remaining chives and cheese, toss to coat and serve immediately.