In a medium saucepan over medium heat, melt 1 cup of brown sugar with 1/4 cup of butter until it becomes smooth and bubbly, about 5 minutes. Pour this mixture evenly into a greased 9x13 inch baking dish.

Slice the brioche bread into thick pieces and arrange these slices vertically, overlapping slightly in the baking dish over the sugar mixture.

In a large mixing bowl, whisk together 5 large eggs, 1 1/2 cups of whole milk, 1/2 cup of heavy cream, 1 tablespoon of vanilla extract, 1/2 teaspoon of ground cinnamon, and 1/4 teaspoon of salt until combined and frothy.

Pour the egg custard mixture over the arranged bread slices and gently press down each slice with a spatula to ensure they are fully soaked. Cover with plastic wrap and refrigerate overnight.

The next morning, preheat your oven to 350°F (175°C) and let the dish sit at room temperature for 20 minutes.

Bake in the preheated oven for 45 minutes until the top is golden brown and a knife inserted in the center comes out clean.

Let the Overnight Crème Brûlée French Toast cool for a few minutes before serving warm, optionally with fresh whipped cream and berries or a drizzle of maple syrup.