In a medium saucepan, combine the chicken livers, onion, garlic, bay leaf, thyme and 1/2 teaspoon of salt. Add the water and bring to a simmer. Cover, reduce the heat to low and cook, stirring occasionally, until the livers are barely pink inside, about 3 minutes. Remove from the heat and let stand, covered, for 5 minutes.
Discard the bay leaf. Using a slotted spoon, transfer the livers, onion and garlic to a food processor; process until coarsely pureed. With the machine on, add the butter, 2 tablespoons at a time, until incorporated. Add the Cognac, season with salt and pepper and process until completely smooth. Scrape the pâté into 2 or 3 large ramekins. Press a piece of plastic wrap directly onto the surface of the pâté and refrigerate until firm. Serve chilled.
MAKE AHEAD
The pâté can be covered with a thin layer of melted butter, then wrapped in plastic and refrigerated for up to 1 week or frozen for up to 2 months.
Special Notes
I removed the veins and other stringy matter to clean the chicken livers. I bought a 20 ounce container from the freezer section of the IGA and it only cost $2.50. I doubled the recipe above except for the butter. I also used more onion and fresh thyme than suggested. I put the pate' in small glass ramekins and it made 5 of them. I let the pate' cool in the refrig covered in plastic then put the melted butter on top and rewrapped in plastic and cooled again.