Prepare a 13x9 inch baking dish with the butter and place the French bread in the dish in slightly overlapping layers. Set aside.
Prepare the custard by whisking together the milk, eggs, dark brown sugar, vanilla extract, cinnamon, and salt until combined.
Pour the custard over the bread, making sure that all the slices are coated well with the custard. Cover tightly with foil and chill overnight in the fridge.
When ready to bake, preheat the oven to 350°F. Bake covered for 40 minutes. Remove the foil and add the pecans. Return to the oven and bake for an additional 15-25 minutes, or until the pecans are toasty and the bread is puffed and beginning to brown.
Serve warm with butter and maple syrup.
Notes
Tip: Get a dense loaf of bread for overnight french toast and cut it yourself for the best results.