In a mixing bowl, whisk together the eggs, milk, sugar, vanilla, and cinnamon until smooth.
Heat a skillet or griddle over medium heat and melt a little butter to coat the surface.
Pour the custard into a shallow dish. Dip each slice of brioche in the mixture, coating both sides briefly. Do not oversoak.
Place the dipped slices on the hot skillet. Cook for 2–3 minutes per side until golden brown and slightly crisp.
Transfer to plates, dust with powdered sugar, drizzle maple syrup, and add your favorite toppings. Serve warm.