Peel the onions and carrots and cut them into medium-sized cubes.
Cut the chicken liver into small pieces.
Pour the vegetable oil into the pan, add the onion and fry over medium heat for 2-3 minutes. Then add the carrots and fry for 10 minutes on low heat.
Add the sliced mushrooms (if using frozen, pre-thaw and drain all the liquid). Cook for another 5 minutes. Transfer to another container.
In a pan, melt the butter, add the chopped liver. Fry on medium heat for 3-4 minutes, stirring occasionally. Add the cognac and fry for 2-3 minutes. Pour in the chicken stock, add the sage, mint, thyme, nutmeg, salt and pepper. Cook for 10 minutes, reducing the heat.
Mix the vegetables with the liver and carefully punch in a blender until pasty. Transfer to a mold and refrigerate for a few hours.