Ingredients
Equipment
Method
Prep and bake
- Preheat the oven to 350°F and grease a 9x5-inch loaf pan. Set up the pan so the batter goes in right after mixing.
- Whisk together the all-purpose flour, baking powder, and salt in a bowl. Whisk until the dry ingredients look evenly combined.
- Cream the softened unsalted butter and granulated sugar until light and fluffy, then beat in the eggs and vanilla extract. Mix just until smooth and visibly paler.
- Alternate adding the flour mixture and sour cream, mixing just until combined. Stop as soon as there are no dry streaks for a tender crumb.
- Pour half the batter into the pan, sprinkle with half the cinnamon sugar topping, then top with the remaining batter and cinnamon sugar. Swirl gently with a knife for thick ribboned pockets.
- Bake for 50–55 minutes, until a toothpick comes out clean. Look for a golden top and set center that springs back lightly.
- Cool in the pan for 10 minutes before slicing. Letting it rest helps the thick cinnamon sugar settle and prevents crumbling.
Notes
Pro tip: for the thick cinnamon sugar swirl, keep the topping fairly packed so it forms visible streaks instead of dissolving. Store tightly wrapped in the refrigerator for up to 4 days; freeze sliced portions for up to 2 months. For a dairy-light option, use plain Greek yogurt in place of sour cream (same amount) for a similar tang and moisture.