Saute the onions in 4 tablespoons butter in a skillet over medium heat for 2 to 3 minutes. Add the chicken livers and cook just until the pink disappears. Remove from heat.
Puree the mixture in a blender or food processor until smooth. Put the egg yolks through a sieve and add to the liver mixture together with the 4 tablespoons softened butter, cream, Cognac, nutmeg, salt and pepper. Process to mix well.
Spoon the pate into a decorative bowl, cover and chill for several hours. Sprinkle the top of the pate with the green onions and chives before serving with toast points or crackers.