Step 1: Preheat and Prepare

Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan and line it with parchment paper for easy removal.

Step 2: Mix the Batter

In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon. In another bowl, combine the buttermilk, melted butter, eggs, and vanilla extract. Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix; a few lumps are okay!

Step 3: Make the Cinnamon Swirl

In a small bowl, mix together the brown sugar and cinnamon. Pour half of the batter into the prepared loaf pan, then sprinkle the cinnamon sugar mixture evenly over the top. Pour the remaining batter on top and use a knife to gently swirl the cinnamon sugar through the batter for that classic marbled effect.

Step 4: Bake

Place the pan in the oven and bake for 45-50 minutes, or until a toothpick inserted in the center comes out clean. Let the bread cool in the pan for about 10 minutes before transferring it to a wire rack.

Step 5: Add the Donut Coating

While the bread is still warm, brush the top with melted butter. Mix the sugar and cinnamon together, then sprinkle (or roll) the bread in this sweet topping. This is what gives it that signature cinnamon-sugar donut taste!