In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, vanilla extract, ground cinnamon, granulated sugar, brown sugar, and salt until well combined.

Arrange the brioche slices in a single layer in a greased 9x13-inch baking dish. Pour the egg mixture evenly over the bread, ensuring each slice is well soaked. Cover with plastic wrap and refrigerate for at least 2 hours, or overnight for best results.

Preheat your oven to 350°F (175°C). Remove the baking dish from the refrigerator and let it sit at room temperature for about 15 minutes.

Bake the French toast for 30-35 minutes, or until it is puffed and golden brown.

Once baked, remove from the oven and let cool for a few minutes. Sprinkle an even layer of granulated sugar over the top.

Using a kitchen torch, carefully caramelize the sugar until it forms a crispy, golden crust. If you don’t have a torch, you can place the dish under the broiler for 1-2 minutes, watching closely to avoid burning.

Allow the caramelized sugar to cool for a minute before serving. Cut into squares and serve warm.