Overnight French Toast
["1/4 c. (1/2 stick) butter, at room temperature", "12 (3/4-inch thick) French bread slices", "6 eggs", "1 1/2 c. milk", "1/4 c. sugar", "2 Tbsp. maple syrup", "1 tsp. vanilla", "1/2 tsp. salt", "powdered sugar", "Maple-Walnut Syrup (recipe follows)"]
["Spread butter over the bottom of a heavy, large baking pan with 1-inch high sides.", "Arrange bread slices in pan."]
["butter", "bread", "eggs", "milk", "sugar", "maple syrup", "vanilla", "salt", "powdered sugar", "Maple"]