Preheat your oven to 350°F (175°C). Grease a loaf pan with cooking spray or a little butter to prevent sticking.

In a large mixing bowl, whisk together the flour, baking powder, baking soda, ground cinnamon, and salt.

In another bowl, beat the eggs, then mix in the melted butter, buttermilk, and granulated sugar until fully combined.

Gradually add the wet mixture into the dry ingredients, stirring until just mixed.

In a small bowl, mix the brown sugar and cinnamon.

Pour half of the batter into the prepared loaf pan. Sprinkle half of the cinnamon-sugar mixture over the top. Pour the remaining batter followed by the rest of the cinnamon-sugar mixture. Using a knife, gently swirl the mixture through the batter.

Bake for about 50-60 minutes or until a toothpick inserted into the center comes out clean.

Let the bread cool in the pan for about 10 minutes. Carefully remove it and let it cool completely on a wire rack before slicing.