Bring a large pot of water to a boil. Add the spinach and cook just until wilted and bright green, a minute or two.
Drain the spinach and rinse under cold water. Squeeze well to remove all excess moisture.
Place the spinach in a large food processor along with the flour and eggs. Process until the mixture comes together and forms a smooth ball. If too wet, add a little more flour. If too crumbly, add a little water.
On a lightly floured surface, knead the dough until soft and elastic. Form into a ball and cover with a damp cloth or wrap in plastic. Allow to rest at room temperature for 30 minutes to one hour.
Divide the dough into four equal pieces. Place one on floured work surface and cover the remainder.
Roll the dough into a thin sheet using a pasta machine or rolling pin, until it is about 1/16th inch thick. Roll through a fettuccine attachment on the pasta machine or cut by hand into ribbons about 1/4 inch wide.
Arrange the fettuccine into small nests on a parchment-lined baking sheet or on a pasta drying rack to dry for a few minutes to an hour. Repeat with remaining dough.
Bring a large pot of salted water to a boil. Add the pasta in batches, careful not to overcrowd, and boil until they rise to the surface. Remove to a colander and drain.
Serve immediately with desired sauce.