Set your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.

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

In a separate bowl, whisk the egg, milk, melted butter (or oil), and vanilla extract until well combined.

Gradually pour the wet ingredients into the dry ingredients, stirring gently until just combined. Do not overmix, as this may affect the texture of the bread.

In a small bowl, mix the brown sugar and additional ground cinnamon. Pour half of the batter into the prepared loaf pan, then sprinkle half of the cinnamon-sugar mixture on top. Repeat with the remaining batter and top with the rest of the cinnamon-sugar mixture.

Use a knife or a skewer to gently swirl the cinnamon mixture into the batter, creating a marbled effect.

Place the loaf pan in the preheated oven and bake for 45-50 minutes, or until a toothpick inserted in the center comes out clean.

Allow the bread to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.

Once cooled, slice and enjoy your delicious homemade cinnamon bread. Serve plain or with butter for extra flavor.