Sprinkle chicken breasts with salt, pepper and paprika to taste. Melt butter over medium heat. Brown chicken breasts on both sides in butter, then add chicken broth, cover and simmer over medium heat until done (about 10 minutes).
In a 5-quart kettle bring 4 quarts salted water to a boil for pasta.
In a blender or food processor blend remaining ingredients until smooth and transfer to top of a double boiler or a metal bowl set over a saucepan of barely simmering water. Heat sauce, stirring constantly, until and instant-read thermometer registers 140°F and remove top of double-boiler of bowl from heat.
Add pasta to boiling water and boil until al dente. Reserve 1/4 cup of the pasta cooking water and drain pasta in a colander. Return pasta to kettle and add sauce and reserved cooking water, tossing gently until combined well. Slice chicken and arrange on top of fettucine and serve.