In a shallow mixing bowl or baking dish, whisk together eggs, milk, sugar, vanilla extract, cinnamon, nutmeg if using, and salt until well combined and smooth.
Heat a grill or cast iron skillet over medium heat. Add 1 tablespoon butter and let it melt, coating the surface.
Working one slice at a time, dip bread into custard mixture, letting it soak for 10-15 seconds per side. Press gently to help bread absorb custard, but don't oversoak or bread will fall apart.
Place soaked bread on hot griddle using tongs or a spatula. Cook for 2-3 minutes until golden brown and crispy on the bottom.
Flip with spatula and cook another 2-3 minutes until the other side is golden brown and custard is fully cooked through.
Transfer cooked French toast to a plate and keep warm in a 200°F oven while cooking remaining slices. Add more butter to griddle between batches as needed.
Serve immediately with a dusting of powdered sugar, drizzle of warm maple syrup, pat of butter, and fresh berries. Add whipped cream if desired.