In a shallow bowl or pie dish, whisk together the eggs, milk, heavy cream, vanilla extract, cinnamon, sugar, and salt until completely smooth and the sugar has dissolved, about 1 minute.
Heat a large nonstick skillet or griddle over medium heat and add 1 tablespoon of butter, swirling to coat the surface evenly.
Dip one slice of brioche into the custard mixture, letting it soak for 30-45 seconds per side until saturated but not falling apart. Gently shake off excess custard.
Place the soaked bread in the hot skillet and cook for 3-4 minutes on the first side, until deep golden brown with crispy edges.
Flip carefully and cook for another 2-3 minutes on the second side until golden and the custard is fully set in the center.
Transfer to a plate and repeat with remaining slices, adding more butter to the pan as needed between batches.
Serve immediately topped with a dusting of powdered sugar and a drizzle of warm maple syrup, or keep warm in a 200°F oven while finishing the remaining slices.
