Preheat the oven: Start by preheating your oven to 350°F (175°C). Grease and flour (or line with parchment) a 9x5-inch loaf pan.
Prepare the crumble topping: In a small bowl, combine the flour, granulated sugar, brown sugar, rolled oats, melted butter, and ground cinnamon. Mix until the ingredients are well combined and crumbly. Set this aside; it's going to be the crowning glory of your bread.
In a medium-sized bowl, whisk together the flour, baking powder, baking soda, salt, and the cinnamon.
In a separate, larger bowl, beat the softened butter and granulated sugar together until the mixture is light and fluffy. This usually takes about 2-3 minutes.
One by one, add the eggs, beating well after each addition. Then, stir in the vanilla extract for an extra layer of flavor.
Gradually add the dry ingredient mixture to the wet ingredients, alternating with the applesauce. Start and finish with the dry ingredients, mixing until just combined.
Gently fold in the diced apples into the batter. You'll love the pockets of tender, juicy apple in every slice.
Pour the apple spice bread batter into the prepared loaf pan. Now, the pièce de résistance: sprinkle the crumble topping evenly over the batter. It's going to add that wonderful texture and a hint of sweetness. If using the extra apple for garnish, cut in half and core and then slice thinly. Push a few slices into the batter with the red skin peeping out.
Pop the pan into the preheated oven and bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean. Be patient; the aroma that fills your kitchen is well worth the wait!
Allow your Crumble Topped Apple Spice Bread to cool in the pan for about 15 minutes before transferring it to a wire rack to cool completely. The hardest part is waiting, but once it's cool, you can slice it and savor the flavors of fall.