Preheat and Prep: Begin by preheating your oven to 350ºF (175ºC). Grease a 9×5-inch loaf pan with butter or oil to prevent the bread from sticking.

Cream the Butter and Sugars: In a large mixing bowl, use a hand mixer or a stand mixer fitted with the paddle attachment to beat the softened butter with granulated sugar and brown sugar. Mix on medium-high speed for 2-3 minutes, or until the mixture becomes light and fluffy.

Add Wet Ingredients: Add the egg, vanilla extract, and buttermilk to the butter and sugar mixture. Mix on low speed until fully incorporated.

Combine Dry Ingredients: Sift the all-purpose flour and baking soda into the bowl with the wet ingredients. Mix gently until the flour is just combined. Use a silicone spatula to fold the mixture, ensuring there are no large lumps.

Prepare the Cinnamon Sugar Mixture: In a small bowl, mix together ⅓ cup of granulated sugar and 1 ½ teaspoons of ground cinnamon. Set aside.

Layer the Batter and Cinnamon Sugar: Pour half of the batter into the prepared loaf pan, spreading it evenly. Sprinkle half of the cinnamon sugar mixture over the batter. Use a butter knife to swirl the cinnamon sugar into the batter gently.

Add Remaining Batter and Topping: Pour the remaining batter over the swirled layer and smooth it out. Sprinkle the rest of the cinnamon sugar mixture on top and swirl again with a butter knife.

Add Melted Butter and Bake: Drizzle 2 tablespoons of melted butter over the top of the loaf. Place the pan in the preheated oven and bake for 50-70 minutes, or until a cake tester or toothpick inserted into the center comes out clean.

Cool and Serve: Allow the bread to cool in the pan for about 20 minutes. Then, carefully remove it from the pan and transfer it to a wire rack to cool completely before slicing and serving.