Preheat & Prep the Pan: Heat your oven to 350°F (175°C). Grease and flour an 8×5-inch loaf pan or line it with parchment paper for easy removal.
Mix Cinnamon Sugar: In a small bowl, combine the brown sugar and cinnamon. You’ll use this to create the swirl and topping.
Whisk Wet Base: In a large bowl, whisk the eggs and granulated sugar until creamy and slightly pale. Stir in melted butter and vanilla extract until smooth.
Combine Dry Ingredients: Add flour, baking powder, baking soda, and salt to the wet mixture. Stir gently until just combined—don’t overmix. The batter should be thick.
Fold in Apples: Gently fold in chopped apples. They should be evenly distributed without breaking down too much.
Layer & Swirl: Pour half of the batter into your prepared pan. Sprinkle about ¾ of your cinnamon sugar mixture evenly over it. Add the remaining batter, then top with the rest of the cinnamon sugar. Use a knife to swirl gently for that marbled look.
(Optional) Add Streusel: If using, sprinkle your crumb topping over the batter before baking.
Bake: Bake for 35–45 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs. If it browns too fast, tent it with foil.
Cool & Slice: Let the bread cool completely in the pan before slicing. This helps set the crumb and prevents crumbling.