Preheat the oven to 350°F. Spray a 10×5-inch loaf pan with nonstick cooking spray. Line with a strip of parchment paper that covers the bottom and hangs over the two long sides.
Peel the apples, then grate them using the largest holes of a box grater. Turn each apple as you reach the core and continue grating until only the core remains. Discard the cores. Measure 2 cups of grated apple and place in a large mixing bowl.
2 cups peeled and grated apples, about 2 medium apples
In a separate bowl, mash the bananas with a fork, then add them to the grated apples.
⅔ cup mashed ripe bananas, about 2 medium bananas
Add the granulated sugar, melted and cooled butter, vanilla, and lightly beaten eggs. Stir until fully combined.
1 ½ cups granulated sugar, ½ cup butter, melted and cooled, 2 teaspoons vanilla extract, 2 eggs, lightly beaten
In a medium bowl, whisk together the flour, baking soda, cinnamon, and salt. Add to the apple mixture and stir just until no streaks of flour remain.
2 cups all-purpose flour, 2 teaspoons baking soda, 2 teaspoons groud cinnamon, 1 ½ teaspoons salt
Transfer the batter to the prepared loaf pan. Sprinkle with the turbinado sugar, if using.
¼ cup turbinado sugar, optional for topping
Bake on the middle rack for 1 hour and 10 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs and no wet batter. If the top is getting too dark before the center is done, loosely cover with foil and continue baking.
Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.