Lightly butter a 9 x 13-inch baking pan or similar-sized casserole dish. Slice a day-old baguette into 3/4- to 1-inch slices. (You'll need about 20 slices to fill the pan.) Place the slices of bread into the pan.
In a medium-sized bowl beat the eggs, then whisk in the milk, sugar, vanilla, nutmeg and salt. Pour this over the bread, and let it soak in while you're preparing the topping.
Peel and slice the apples thinly. Toss them with the remaining ingredients, and spread them over the bread in the pan.
Bake the French toast in a preheated 375°F oven for 30 to 40 minutes, until the apples are soft and the eggs set. Serve warm, in squares, accompanied by bacon or sausage, of desired.