Slice the brioche bread into thick slices, about 1 inch each, and place them in a greased 9x13 inch baking dish vertically or in a single layer if possible.
In a mixing bowl, whisk together the eggs, whole milk, heavy cream, 1 cup of granulated sugar, vanilla extract, ground cinnamon, and salt until well combined.
Pour the custard mixture evenly over the brioche slices, ensuring each piece is well saturated. Cover the dish with plastic wrap and refrigerate overnight (at least 6 hours).
Preheat your oven to 350°F (175°C).
Remove the plastic wrap and bake the French toast for about 30 minutes, or until it’s set and lightly golden on top.
Once baked, remove from the oven and let it cool for about 5-10 minutes.
Sprinkle the additional ¼ cup of granulated sugar evenly over the top of the French toast.
Using a kitchen torch, caramelize the sugar until it is golden and crispy. If you do not have a torch, you can place the baking dish under the broiler for a few minutes but keep a close eye on it to avoid burning.
Let the caramelized sugar cool for a couple of minutes before serving. Cut into squares and enjoy!