Adjust one oven rack to lowest position in oven, and top rack about 6" from broiler element. Preheat oven to 425 degrees F. Coat the bottom of a rimmed baking sheet with cooking spray or vegetable oil to prevent sticking.
In a large bowl, whisk eggs, vanilla, sugar, cinnamon and salt in a large bowl until the sugar is dissolved, and mixture is smooth with no streaks of eggs. Whisk in melted butter until completely blended, then whisk in milk.
Pour the egg mixture in the bottom of the baking sheet. Place bread slices in egg mixture. Once all the slices of bread are on the baking sheet, flip them over starting with the one you placed down first. This will ensure that each slice is perfectly coated. Let the bread slices soak up all the remaining custard, about one minute.
Place baking sheet on the lower rack and bake French toast until bottoms are golden brown, about 10 to 15 minutes. While the French toasting is baking, prepare the banana topping.
Transfer sheet to upper rack and turn the broiler on, leaving the baking sheet in the oven while it's heating. Broil until the tops are golden brown. Rotate baking sheet if necessary, about 1 to 4 minutes.