Preheat the Oven:

Preheat your oven to 350°F (175°C). Grease and flour your loaf pan, or line it with parchment paper.

Prepare the Cinnamon Sugar Swirl:

In a small bowl, mix together the granulated sugar and cinnamon. Set aside.

Mix the Dry Ingredients:

In a large bowl, whisk together the flour, granulated sugar, brown sugar, baking powder, baking soda, salt, cinnamon, and nutmeg.

Prepare the Wet Ingredients:

In another bowl, mix the melted butter, eggs, sour cream, and vanilla extract until well combined.

Combine the Mixtures:

Gradually add the wet ingredients to the dry ingredients, stirring just until combined.

Fold in the diced apples.

Assemble the Bread:

Pour half of the batter into the prepared loaf pan. Sprinkle half of the cinnamon sugar mixture over the batter.

Pour the remaining batter on top and sprinkle with the remaining cinnamon sugar mixture. Use a knife or skewer to swirl the cinnamon sugar into the batter, creating a marble effect.

Bake the Bread:

Bake in the preheated oven for 50-60 minutes, or until a toothpick inserted into the center comes out clean.

If the top starts to brown too quickly, cover loosely with aluminum foil.

Cool and Glaze:

Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

If desired, mix powdered sugar, milk, and vanilla extract to make a glaze. Drizzle over the cooled bread.