Ingredients
Method
- Make the Streusel: Combine flour, brown sugar, cinnamon, and sea salt in a small bowl. Drizzle melted butter over the top and stir with a fork until large, uneven clumps form. Cover and refrigerate while you prepare the rest of the batter.
- Make the Cinnamon Swirl: Stir together the brown sugar and cinnamon in a small bowl until no lumps remain. Set aside.
- Cream Butter and Sugar: Beat the room-temperature butter and granulated sugar together on medium speed with a hand mixer for 4 to 5 full minutes, until the mixture is pale, nearly white, and noticeably fluffy. Scrape down the sides and bottom of the bowl at least twice during this step.
- Add Wet Ingredients: Add the eggs, sour cream, and vanilla extract to the creamed butter mixture. Mix on medium-low speed for about 30 seconds until smooth and cohesive. The batter may look slightly curdled at first — keep mixing and it will come together.
- Fold in Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Add the dry ingredients to the wet mixture along with the milk. Switch to a rubber spatula and fold gently just until no streaks of flour remain — about 12 to 15 folds. Do not over-mix.
- Preheat and Prepare Pan: Preheat your oven to 325°F (163°C). Line a 9x5-inch loaf pan with parchment paper, leaving overhang on the long sides. Lightly spray with nonstick spray.
- Assemble the Loaf: Spread half the batter evenly into the prepared pan. Sprinkle the entire cinnamon-sugar swirl over the surface. Cover with the remaining batter and smooth the top. Remove the streusel from the fridge, break into large crumbles with a fork, and scatter generously over the top.
- Bake: Bake at 325°F for 60 to 70 minutes, until a skewer inserted into the center comes out clean or with just a dry crumb. Start checking at the 60-minute mark.
- Cool: Let the loaf cool in the pan for 10 minutes. Use the parchment overhang to lift it onto a wire rack. Wait at least 20 more minutes before slicing to preserve the clean cinnamon ribbon in the center.
Notes
All dairy and eggs must be at room temperature before you begin — cold ingredients cause the batter to curdle.
Use a light-colored metal loaf pan. Dark pans can overbake the edges before the center sets.
Never skip chilling the streusel. Even 15 minutes in the fridge is enough to keep it crunchy and defined on top.
Measure flour by spooning into the cup and leveling — scooping directly can add up to 20% extra flour.
Storage: Wrap cooled loaf in parchment then plastic wrap. Keeps at room temperature for up to 3 days. Freeze whole or in slices for up to 3 months.
Greek Yogurt Swap: Full-fat plain Greek yogurt can replace sour cream in a pinch. Avoid nonfat versions.