Prepare the Custard: In a large, shallow bowl, vigorously whisk the eggs until smooth. Add the slightly melted ice cream and whisk persistently until the mixture is completely smooth and homogenous. Whisk in the cinnamon, vanilla extract (if using), and salt.
Soak the Bread: Dip each slice of bread into the custard mixture, allowing it to soak for 20-30 seconds per side. The bread should feel heavy and fully saturated but still hold its shape.
Cook to Perfection: Heat a large non-stick skillet or griddle over medium heat. Add 1 tablespoon of butter. Once melted and foaming, add the soaked bread slices (do not overcrowd). Cook for 2-4 minutes per side, until deeply golden brown and crisp. Add more butter for subsequent batches.
Serve Immediately: Plate the French toast immediately. Dust with confectioners' sugar, top with fresh berries, and serve with warm maple syrup on the side. For the ultimate indulgence, add a scoop of cold vanilla ice cream on top to contrast the warm toast.