Cream together butter and sugar. Add eggs and vanilla, mixing well.
Whisk together flour, baking soda, and salt. Alternate adding dry ingredients and sour cream/milk to the butter mixture. Fold in apples.
Pour half the batter into a loaf pan. Mix cinnamon swirl ingredients and sprinkle over batter. Top with remaining batter.
Mix topping ingredients and sprinkle over the batter.
Bake at 350°F (175°C) for 50-60 minutes or until a toothpick comes out clean.
Prep Time: 15 minutes | Cooking Time: 60 minutes | Total Time: 1 hour 15 minutes | Kcal: 325 kcal