For the pasta with Gorgonzola sauce, cook penne in hot salted water for 12-15 minutes.
Peel and finely dice the onion. Heat fat in a small saucepan, add onions and sauté until translucent. Deglaze with whipping cream, bring to a boil and simmer over low heat, stirring, for 2-3 minutes.
Cut sage, except for a few leaves for garnish, into tender strips. Coarsely dice gorgonzola. Add sage and bouillon cubes to sauce.
Add sauce thickener, stirring constantly, and bring to a boil. Add Gorgonzola and bring to a boil again.
Season the sauce with salt and pepper. Chop walnuts. Strain pasta, drain and arrange on plates with sauce. Sprinkle with chopped walnuts and garnish with sage.