Preheat the oven to 300 degrees F (150 degrees C).
Place Brioche (8 slice) on a wire rack set on a rimmed baking sheet. Bake the slices for 15 minutes, flipping halfway through the baking process. Once ready, remove bread from the rack and set it aside to cool.
Turn the heat down to 200 degrees F (95 degrees C). Return the baking sheet back into the oven.
Crack the Egg (3) and separate the egg yolks from the egg whites. Reserve the 3 egg yolks for the next step.
Whisk together the Milk (1 1/2 cup), egg yolks, Brown Sugar (2 tablespoon), Unsalted Butter (2 tablespoon), Vanilla Extract (1 tablespoon), Ground Cinnamon (1/2 teaspoon), and Salt (1/4 teaspoon) in a large, flat Pyrex.
Soak 1 slice at a time into the milk mixture – 20 seconds long on each side for each slice. It should be wet, not falling apart. Let the excess milk mixture drip off. Place it on a baking sheet lined with parchment paper. Repeat the same process with the rest of the slices.
Heat Unsalted Butter (1/2 tablespoon) in a large (12-inch) non-stick skillet, over medium heat.
Using a slotted spatula, transfer 2 slices of Brioche on to the skillet, and cook for 3-4 minutes on each side or until they turn golden brown. If they turn golden brown too quickly turn down to heat just a little.
Place cooked slices onto the baking sheet in the oven to keep them warm until you are ready to eat.
Repeat the same process for the rest of the Brioche slices using 1/2 tablespoon of Unsalted Butter (1 1/2 tablespoon) each time.
To assemble: Place a slice of French Toast in the middle of a plate. Spread 1/2 tablespoon (or more) Mascarpone Cheese (3 tablespoon) on top and sprinkle it with Pistachios (1/4 cup).
Stack a second French Toast on top, and repeat the same process. Place the third slice on top of the second one, and top it off with your favorite Fresh Mixed Berries (1 cup).
Drizzle it with Caramel Sauce (1/2 cup) and sprinkle it with Powdered Confectioners Sugar (2 tablespoon) and some more pistachios.