01 - Butter a 9x13-inch baking dish generously. Arrange French bread slices in a single layer, overlapping only as needed.
02 - In a large bowl, whisk eggs, half-and-half, milk, vanilla extract, granulated sugar, ground cinnamon, and ground nutmeg until smooth and fully incorporated.
03 - Pour custard mixture evenly over bread slices, ensuring each slice is coated. Gently press bread into the custard to guarantee full absorption.
04 - Cover the dish tightly with plastic wrap and refrigerate overnight to allow bread to soak and flavors to develop.
05 - Preheat oven to 350°F. Remove baking dish from refrigerator and take off plastic wrap. Scatter butter pieces across the top and sprinkle a light layer of granulated sugar. Bake for 35 to 40 minutes, until puffed and golden brown.
06 - Allow baked French toast to cool slightly. Evenly scatter granulated sugar over the top. Using a kitchen torch or oven broiler, caramelize the sugar until golden and crisp.
07 - Let cool for several minutes. Portion and transfer to individual plates, drizzle with maple syrup, and serve immediately.