Prepare the Caramel Base: In a small saucepan over medium heat, melt the butter. Stir in the brown sugar and corn syrup until smooth. Pour the mixture into a greased 9x13-inch baking dish and spread evenly.
Assemble the French Toast: Slice the bread into thick slices (about 1 inch). Arrange the bread slices on top of the caramel base in a single layer, slightly overlapping if necessary.
Make the Custard: In a large bowl, whisk together eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and salt. Pour the custard evenly over the bread slices, ensuring each slice is well coated. Cover with plastic wrap and refrigerate overnight (or at least 6 hours).
Bake: Preheat oven to 350°F (175°C). Remove the dish from the refrigerator 30 minutes before baking. Bake uncovered for 35–40 minutes or until golden and set.
Add the Brûlée Topping: Sprinkle granulated sugar evenly over the top of the baked French toast. Use a kitchen torch to caramelize the sugar until it forms a golden crust. Alternative: If you don’t have a torch, place the dish under the broiler for 1–2 minutes until the sugar melts and browns (watch closely!).
Serve: Let cool for a few minutes to allow the caramel to set. Slice and serve warm with a drizzle of maple syrup or fresh berries if desired.