Bring a large pot of water to a boil; add about 1 Tbs. salt.
In a large skillet, combine the butter and sage. Stir over low heat until the butter has melted.
Add the cream and stock and bring to a boil; cook until the mixture lightly coats the back of a spoon, about 3 minute
Season with salt and pepper.
Remove the sauce from the heat but keep it warm.
Meanwhile, cook the fettuccine until al dente, 10 to 12 minute
With tongs, lift the pasta from the pot, let it drain for a moment over the boiling water, and then add it to the sauce in the skillet. (Alternatively, drain the pasta in a colander and add it to the sauce.)
Cook gently on low for a few minutes for the pasta to absorb the sauce.
Remove the pasta from the heat and stir in the grated cheese, and season amply with pepper.
Serve in warmed bowls topped with the shaved ricotta.