Combine the melted butter, coconut sugar, and maple syrup in a small bowl. Stir until they are completely mixed. Spread 1/2 of the mixture into a 10" cast iron skillet.
Beat together the eggs, milk, vanilla, cinnamon, and salt in a large mixing bowl. Take each slice of bread and dip it into the mixture, then arrange the slices in the skillet. Layer the bread slices as needed until you have dipped and arranged all the slices in the loaf.
Spread the remaining butter and sugar mixture over the tops of the arranged bread slices. Cover the French toast and let it set in the fridge for 1 hour.
Preheat the oven to 375°F. Uncover and bake the French toast for 35-40 minutes. The French toast should be firm and brown around the edges. Serve warm with additional maple syrup!
Notes: If baking immediately, let the French toast set at room temperature for 10-15 minutes prior to baking. If preparing the night before, don't dip the bread slices in the egg mixture. Simply arrange the slices in the skillet and pour the egg mixture ontop.