01 - Melt butter with brown sugar and corn syrup in a small saucepan over medium heat, stirring constantly until smooth and bubbling. Pour mixture into the bottom of a 9x13-inch baking dish and spread evenly.
02 - Place bread slices in a single layer over the caramel, arranging them snugly with slight overlap if necessary to fit the dish.
03 - Whisk together eggs, milk, heavy cream, granulated sugar, vanilla extract, and salt in a large mixing bowl until completely smooth and well combined.
04 - Evenly pour the custard mixture over the bread slices. Gently press down on the bread with your hands or a spatula to help absorb the liquid.
05 - Cover the baking dish tightly with plastic wrap and refrigerate for 8 to 12 hours to allow the bread to fully soak up the custard.
06 - Remove the dish from the refrigerator and let it sit at room temperature while you preheat the oven to 350°F.
07 - Bake uncovered for 30 to 35 minutes until the French toast is puffed, golden brown, and the custard is completely set.
08 - Let the dish cool for 5 minutes after removing from the oven.
09 - Sprinkle the remaining 1/4 cup granulated sugar evenly over the top. Use a kitchen torch to melt and caramelize the sugar until it forms a crispy, 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.