In a large skillet, melt 4 Tbl butter. Add Onions and cook until soft, about 3 minutes. Add garlic and cook until fragrant, about 30 seconds.
Add Chicken Livers, bay leaves, thyme, salt, pepper and cook until the livers are browned on the outside and slightly pink on the inside, about 5 minutes. add Cognac and and cook until most of the liquid is evaporated and the livers are cooked through but still tender. Remove from heat and allow to cool slightly. Discard bay leaves.
Puree the mixture in a food procesor. Add the remaining butter in pueces and pulse to blend.
Pack into 6 ramekins , about 4oz. each. Cover with plastic and refrigerate until firm (6 hours)