Baked Overnight French Toast

1/4 cup butter, room temperature
12 3/4 inch slices French bread
6 eggs
1 1/2 cups milk
1/4 cup sugar
2 tablespoons maple syrup
1 teaspoon vanilla
1/2 teaspoon salt
Powdered sugar

In large bowl beat eggs, milk, sugar, syrup, vanilla and salt to blend. Pour mixture over bread. Turn bread slices to coat. Cover with plastic and refrigerate overnight.
In the morning, preheat oven to 400F degrees.
Spread butter over bottom of heavy large baking pan with 1 inch sides. Remove bread from egg mixture and arrange slices in pan.
Bake French bread 10 minutes. Turn bread over and continue baking until just golden, about 4 minutes longer.
Transfer cooked toast to plates and sprinkle with powdered sugar. Serve at once with warm maple syrup and chopped, toasted walnuts.