• Preheat & prepare pan.

  Heat the oven to 350°F (175°C). Grease and line a 9×5-inch loaf pan with parchment paper, leaving some overhang for easy lifting.

  Mix the dry ingredients.

  In a medium bowl, whisk together the flour, baking powder, apple pie spice, and salt. Set aside.

  Toss the apples.

  In a small bowl, stir together the diced apples, sugar, and apple pie spice. Toss until evenly coated. Set aside.

  Make the swirl.

  In another bowl, mix the brown sugar and Saigon cinnamon for the swirl. Set aside.

  Build the base batter.

  In a large bowl, whisk the melted butter with the brown sugar and cane sugar until glossy and smooth. Add the eggs, one at a time, whisking well after each. Stir in the vanilla, then whisk in the sour cream until creamy and well blended.

  Combine wet and dry.

  Add the dry mixture to the wet ingredients. Fold gently with a spatula just until no streaks of flour remain. Do not overmix.

  Fold in the apples.

  Add the apple mixture (and any juices) to the batter and fold until evenly distributed.

  Assemble the loaf.

  Spread half the batter evenly in the prepared pan. Sprinkle half of the swirl mixture over the top. Add the remaining batter, smooth it gently, then sprinkle with the remaining swirl mixture. Drag a butter knife through the batter in a few swirls to marble it lightly.

  Bake.

  Bake for 55–65 minutes, until a toothpick inserted in the center comes out clean or with just a few moist crumbs. Tent loosely with foil after 40 minutes if the top browns too quickly.

  Cool completely.

  Allow the bread to cool in the pan for 15 minutes before lifting it onto a wire rack. Let the loaf cool completely before glazing.

  Glaze.

  In a small bowl, whisk together the powdered sugar, milk, and vanilla until smooth and pourable. Drizzle generously over the cooled bread.

Notes & Serving

• Flavor: Saigon cinnamon is bold, sweet, and aromatic, which makes it perfect here—don’t substitute with mild Ceylon cinnamon.

  Serving: This bread slices best once fully cooled, but if you sneak a piece early you’ll get gooey, sticky swirls of sugar.

  Storage: Keep covered at room temperature for up to 3 days, or freeze slices individually for up to 2 months.