1Melt butter in 1-quart saucepan over medium heat. Cook leeks in butter about 3 minutes, stirring frequently, until softened; remove from heat.
2Cut enough bread into 1-inch cubes to measure 5 cups. Mix bread cubes, leeks, chicken and dill weed. Spread bread mixture in ungreased square baking dish, 8x8x2 inches. Sprinkle with cheese. Mix remaining ingredients; pour over cheese. Cover tightly and refrigerate at least 4 hours but no longer than 24 hours.
3Heat oven to 325°F. Uncover and bake 50 to 55 minutes or until knife inserted in center comes out clean. Let stand 10 minutes before cutting.