Combine chicken livers, onion, stock, bay leaf, thyme and 1/2 teaspoon salt in medium saucepan. Heat to boil over medium heat; reduce heat to low. Barely simmer, covered, until livers are just tender, 6-8 minutes. Remove from heat; let stand 10 minutes. Drain, discard bay leaf. Put liver, butter, cognac, salt, pepper and ginger into food process or blender. (If using blender, process in two batches.) Process with on/off turns until smooth. Transfer to large bowl; stir in nuts. Refrigerate covered, 15 minutes. Fold whipping cream into liver mixture. Taste and adjust seasoning. Spoon into 3 cup terrine, packing slightly. Refrigerate covered at least 24 hours, or up to 1 week.