Preheat your oven to 175°C (350°F). Grease and flour a 9x5-inch loaf pan, or line it with parchment paper with some extra hanging over the sides for easy lifting.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon. Set aside.
In a large mixing bowl, cream the softened butter and sugar until light and fluffy using a hand mixer or stand mixer.
Add the yogurt and vanilla extract to the creamed mixture. Beat well until smooth and combined.
Add the dry ingredients in three additions, alternating with the buttermilk in two additions—starting and ending with the dry ingredients. Mix on low speed and scrape down the sides of the bowl as needed. Towards the end, switch to a spatula and gently fold to finish mixing. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top evenly with a spatula.
In a small bowl, mix together the cinnamon and sugar for the topping. If desired, brush the top of the batter with melted butter, then sprinkle the cinnamon sugar mixture evenly over it.
Bake for 50–55 minutes, or until a toothpick inserted into the center of the bread comes out clean or with a few moist crumbs.
Let the bread sit in the pan for 5 minutes to cool slightly. Then, remove the bread from the pan using the parchment paper overhang.
In a small bowl, mix together the sugar and cinnamon for the topping.
Brush the warm bread with melted butter.
Place the bread in a large shallow dish and sprinkle the cinnamon-sugar mixture generously over the bread for easy coating.
Transfer the bread to a wire rack and let it cool completely before slicing.
Notes
Softened Butter: Makes it easier to cream with sugar and helps create a light, tender crumb.
Buttermilk Substitute: Mix ½ cup milk with ½ tablespoon vinegar or lemon juice. Let sit for 5 minutes before using.
Sugar: Use caster sugar or brown sugar for a softer, more caramel-like flavor.
Storage: Store at room temperature for up to 2 days or refrigerate up to 5 days in an airtight container. Can be frozen for longer storage.