Crumble chestnuts into the onions and cook with a little olive oil and water. The chestnuts should be moist. Add the roasted garlic and cognac and allow the alcohol to burn off.
Pour ingredients into a food processor and process until smooth, adding olive oil until desired consistency is achieved (should be relatively thick). You can run this through a fine seive for a smooth pate, or leave it chunky. If you want this more of terrine style, you may set the pate with a little gelatin.
Serve with my whole wheat flatbreads. http://www.foodista.com/recipe/VMPL7WNX/evas-whole-wheat-flatbread