Preheat your oven to 350°F (175°C) and grease a loaf pan. In a large mixing bowl, combine the flour, sugar, baking powder, baking soda, cinnamon, and salt. In another bowl, whisk together the eggs, buttermilk, melted butter, and vanilla extract until well combined. Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Pour the batter into the prepared loaf pan and smooth the top. In a small bowl, mix together the topping sugar and cinnamon, then sprinkle it evenly over the batter. Bake for 50-60 minutes or until a toothpick inserted in the center comes out clean. Let it cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
