How To Make Cinnamon Swirl Apple Fritter Bread:
Preheat the oven to 350˚F. Line a loaf pan with parchment paper and set aside.
Prepare the filling/topping. In a small bowl, combine brown sugar, cinnamon, and optional nutmeg. Mix to combine and set aside.
Create the cake batter. In a large bowl, combine sugar, melted butter, sour cream, eggs, milk, and vanilla extract. Mix by hand or use an electric mixer until ingredients are well combined and smooth. Set aside.
In a separate bowl, combine flour, baking powder, baking soda, and salt. Mix to combine.
Add the dry ingredients to the wet ingredients, mixing until just combined (avoid overmixing).
Peel, core, and chop the Granny Smith apple into 1/2-inch cubes.
Fold all but a handful of the chopped apples into the batter.
Pour half of the batter into the prepared loaf pan, spreading it into a single layer.
Add half of the cinnamon sugar filling on top and smooth it out. Use a flat butter knife to create swirls through the batter.