Preheat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan and set aside.
In a medium bowl, whisk together the all-purpose flour, baking soda, cream of tartar, salt, and ground cinnamon. Set aside.
In a large bowl, use an electric mixer to cream the softened unsalted butter and 1 cup granulated sugar until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Stir in the mashed bananas and sour cream until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
In a small bowl, combine 2 tablespoons granulated sugar and 1 teaspoon ground cinnamon. Sprinkle this cinnamon-sugar mixture evenly over the top of the batter.
Bake in the preheated oven for 55 to 65 minutes, or until a toothpick inserted into the center comes out clean.
Remove the bread from the oven and allow it to cool in the pan for 10 minutes.
Transfer the bread to a wire rack to cool completely before slicing and serving.