Preheat oven to 350 F. Butter a 1-1/2 quart baking dish. Place bread cubes in baking dish. Mix and heat milk, sugar and butter just enough to dissolve sugar and melt butter. Beat eggs slightly, adding salt. Stir eggs into warm milk and add vanilla. Pour liquid mixture over bread cubes and set baking dish in a pan of hot water. Bake 1 hour or until knife inserted in center comes out clean. To make sauce, combine sugar, cornstarch and salt. Stir in water, boil 1 minute. Remove from heat and stir in butter and lemon juice. Serve pudding hot with lemon sauce.