Whisk the eggs in a wide, shallow dish until no streaks of white remain. Whisk in the milk, maple syrup, vanilla, cinnamon, nutmeg and salt.
Heat the oven to 200°F (95°C) and place a baking sheet with a rack inside to keep the finished toast warm.
Heat a large skillet or griddle over medium to medium-low heat and melt a little butter.
Dip two slices of bread at a time into the custard, letting each side soak for 15–30 seconds, depending on how dense the bread is. Let any excess drip off.
Cook the slices for 3–4 minutes per side, until deep golden brown and slightly puffed. Adjust the heat if they brown too quickly.
Transfer to the oven while you cook the rest, adding butter to the pan as needed. Serve warm with your favorite toppings.