01 - Melt butter with brown sugar and corn syrup in a small saucepan over medium heat. Stir continuously until mixture is smooth and bubbling. Pour caramel evenly into the bottom of a 9x13-inch baking dish.
02 - Place bread slices in a single layer over the caramel, allowing slight overlap 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 - Pour custard mixture evenly over bread slices. Gently press bread down with spatula to ensure thorough absorption of liquid.
05 - Cover baking dish tightly with plastic wrap. Refrigerate for 8 to 12 hours to allow bread to fully absorb custard and develop flavor.
06 - Remove dish from refrigerator and let stand at room temperature while oven preheats to 350°F.
07 - Bake uncovered for 30 to 35 minutes until French toast is puffed, golden brown, and custard is completely set in center.
08 - Let baked French toast rest for 5 minutes before proceeding with sugar topping.
09 - Sprinkle granulated sugar evenly over surface. Using kitchen torch, melt and caramelize sugar until deep golden brown and bubbly. Alternatively, place under broiler for 1 to 2 minutes, watching closely to prevent burning.
10 - Serve warm, spooning caramel sauce from bottom of dish over each portion.