Step 1: Prepare the Cinnamon Swirl

• In a small bowl, mix together brown sugar and 1 teaspoon of cinnamon.
• Set aside to layer in the bread batter later.

Step 2: Prepare the Batter

• Preheat your oven to 350°F (175°C). Grease and flour a loaf pan.
• In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, salt, and remaining 1 teaspoon of cinnamon.
• In another bowl, melt the butter and let it cool slightly. Then, whisk in eggs, vanilla extract, milk, and sour cream or yogurt.
• Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Be careful not to overmix.

Step 3: Layer the Batter and Cinnamon Swirl

• Pour half of the batter into the prepared loaf pan.
• Sprinkle half of the cinnamon sugar mixture evenly over the batter.
• Add the remaining batter on top, followed by the rest of the cinnamon sugar mixture.
• Use a knife or skewer to gently swirl the cinnamon sugar into the batter, creating a marbled effect.

Step 4: Bake the Bread

• Place the loaf pan in the oven and bake for 45-55 minutes, or until a toothpick inserted in the center comes out clean.
• Let the bread cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.

Step 5: (Optional) Prepare the Glaze

• In a small bowl, whisk together powdered sugar and a few tablespoons of milk or heavy cream until smooth.
• Drizzle the glaze over the cooled bread before slicing and serving.