01 - Melt butter with brown sugar and corn syrup in a small saucepan over medium heat, stirring constantly until smooth and bubbling. Pour the mixture into the bottom of a 9x13-inch baking dish and spread evenly across the surface.
02 - Place bread slices in a single layer over the caramel, arranging them in a slightly overlapping pattern if necessary to fit the entire loaf.
03 - Whisk together eggs, milk, cream, sugar, vanilla extract, and salt in a large mixing bowl until completely smooth and well combined.
04 - Pour the custard mixture evenly over the arranged bread slices. Gently press down on the bread with your hands or a spatula to help it absorb the liquid.
05 - Cover the baking dish tightly with plastic wrap and refrigerate for 8 to 12 hours, preferably overnight, to allow the bread to fully absorb the custard.
06 - Preheat the oven to 350°F. Remove the dish from the refrigerator and let it sit at room temperature while the oven heats, about 15 to 20 minutes.
07 - Bake uncovered for 30 to 35 minutes, or until the French toast is puffed, golden brown on top, and the custard is completely set.
08 - Remove from the oven and let the dish cool for 5 minutes before proceeding with the topping.
09 - Sprinkle granulated sugar evenly over the entire surface. Use a kitchen torch to melt and caramelize the sugar until it forms a crisp, golden crust. Alternatively, place under the broiler for 1 to 2 minutes, watching closely to prevent burning.
10 - Serve warm, spooning any extra caramel sauce from the bottom of the dish over each portion.