Preheat your oven to 350 degrees F. Grease the inside of an 8-inch x 4-inch loaf pan. Set aside.
In a small mixing bowl, stir together the flour, baking powder, and salt. Set aside.
In a large bowl, beat together the butter and sugar until light and fluffy, about 1 minute. Then add in the eggs, vanilla, and sour cream and mix until smooth.
Add half of the flour mixture to the bowl and mix. Then add half of the milk and mix again. Repeat until the rest of the dry ingredients and milk have been incorporated into the batter.
Remove 1 cup of the batter to a small bowl. Stir in the cinnamon and molasses until combined.
Add half of the vanilla batter to the prepared loaf pan. Top with all of the cinnamon batter. Then pour the remaining vanilla batter on top. You can bake as is or use a butter knife to swirl the layers together a bit.
Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out clean (with a few crumbs is okay, but not with wet batter).
Remove from the oven and allow the bread to cool in the pan for 10 minutes. Then run a knife around the edge, remove it from the pan, and transfer it to a wire rack to finish cooling completely. (Make sure the loaf is cooled completely before attempting to move onto the nest step. Otherwise, it will be too soft and could break when you try to lift and dip it.)
Topping
Mix the sugar, brown sugar, and cinnamon on a large plate. Spread the mixture into an even layer. Brush the entire outside loaf with melted butter and then dip all sides into the sugar mixture. Cut into slices and enjoy!
Notes
Nutritional information is based on 1 loaf cut into 8 slices.