Slice the French bread or challah in 1-inch thick slices. Save the rest of the loaf for another use.

Whisk the eggs with the half-and-half or whole milk in a large bowl or baking dish. Whisk in the powdered sugar, vanilla, cinnamon, nutmeg, and kosher salt until smooth. Set aside.

Melt the butter and oil in a large non-stick skillet between medium and medium-high heat or set an electric frying pan to 350°F. Dip 4 bread slices in the egg mixture, coating both sides well. Soak the bread for 3-5 minutes up to 15 minutes. Let the excess egg drip from the bread before adding to the skillet in an even layer. Cook for 3-4 minutes or until golden, then flip and cook for 3-4 more minutes. Transfer to a serving platter. Add more oil or butter to the skillet if needed and repeat with the rest of the bread slices.

Serve the French toast slices hot topped with butter and drizzled with maple syrup.