Preheat your oven to 350°F (175°C).
In a large mixing bowl, whisk together the eggs, heavy cream, whole milk, granulated sugar, vanilla extract, and cinnamon until well combined.
Slice the brioche bread into thick slices, about 1 inch each.
Submerge the bread slices into the custard mixture, allowing them to soak for at least 10 minutes, turning occasionally.
Heat butter in a skillet over medium heat. Once melted, add soaked bread slices, cooking for 3-4 minutes per side or until golden brown.
Transfer the cooked slices to a baking dish and bake in the preheated oven for 10-15 minutes, until set.
Remove from the oven and let cool slightly before serving.
Sprinkle an even layer of sugar over the top of each slice, then use a kitchen torch to caramelize the sugar until golden and crispy.
Serve immediately, garnished with fresh berries or whipped cream, if desired.