Preheat oven to 350°F. Grease a 9x13-inch baking dish.
In a large bowl, whisk together eggs, half & half, milk, sugar, cinnamon, vanilla, nutmeg, and salt until smooth.
Arrange the sliced challah in the prepared baking dish, slightly overlapping. Pour the custard evenly over the bread, pressing down gently so each piece soaks it up. Let sit for 10–15 minutes.
In a small bowl, mix together the chopped pecans, melted butter, cinnamon, nutmeg, and salt. Sprinkle evenly over the soaked challah.
Bake for 30–40 minutes, until the custard is set and the top is golden brown.
Let cool for 5 minutes, then serve warm drizzled with caramel sauce and maple syrup.