Cooking pasta in stock is a fabulous alternative to using your stock for soup. The pasta absorbs the flavors from the stock and leaches out starch, which thickens the stock to create a savory sauce. You can cook the pasta up saucy and soupy with more stock, or tight and dry with less stock. Both versions are delicious and versatile. It is best to use thin spaghetti (spaghettini) or thin linguini (linguini fini). They will absorb the stock more efficiently. Thicker pasta will work, but you will need more stock and the taste will be wheaty. Very thin pasta like fidelini is good, but it absorbs fast, and tends to get knotted and overcooked. If I use stock to cook fidelini, I prefer to serve it as a soup.
You will need about 1 pint of stock for every ¼ pound of pasta. You can use any kind of stock: asparagus stock (though it may need to be thinned some), mushroom stock (made from mushroom stems or dried mushrooms), poultry, beef, or fish stock. Bring the stock to a boil in your pasta pot over a medium high heat. Season the stock to taste. Add the pasta. It will be stiff and stick out of the stock. Be patient. Gently push down the pasta, and after about 5 minutes it will soften and collapse into the stock. Stir often, as the pasta tends to stick together. Cook the pasta in the stock until it is al dente. You will notice the starch from the pasta thickens the stock to create a sauce. Add a little more stock or water if the sauce gets sticky. Do not overcook the pasta. It is best to serve this pasta loose.