01 - Melt butter with brown sugar and corn syrup in a small saucepan over medium heat, stirring constantly until smooth and bubbling. Pour caramel 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, heavy cream, granulated sugar, vanilla extract, and salt in a large mixing bowl until completely smooth and well combined.
04 - Distribute custard mixture evenly over the bread slices. Gently press down on each piece of bread to ensure thorough absorption of the liquid.
05 - Cover baking dish tightly with plastic wrap. Refrigerate for 8 to 12 hours to allow bread to fully absorb the custard and develop optimal texture.
06 - Preheat oven to 350°F. Remove dish from refrigerator and let stand at room temperature while oven heats, approximately 15 to 20 minutes.
07 - Bake uncovered for 30 to 35 minutes until the French toast is puffed, golden brown, and the custard is completely set. A knife inserted near the center should come out clean.
08 - Remove from oven and let cool for 5 minutes. This brief resting period allows the custard to firm slightly for easier handling.
09 - Sprinkle granulated sugar evenly over the entire surface. Using a kitchen torch, melt and caramelize the sugar until deep golden brown and bubbly. Alternatively, place under a broiler for 1 to 2 minutes, watching closely to prevent burning.
10 - Serve warm, spooning any remaining caramel sauce from the bottom of the dish over each portion.