Preheat oven to 350°F. Grease a 9 x 5-inch loaf pan.
Whisk oil, sugar, egg, sour cream and vanilla in a large bowl. Whisk in buttermilk, then flour, baking powder, baking soda and salt. Pour half of the batter into prepared pan.
Combine brown sugar and cinnamon in a small bowl. Sprinkle ½ of the sugar mixture over batter; pour remaining batter evenly over top. Sprinkle remaining sugar mixture on top. Using a knife, swirl through batter.
Bake 50-60 minutes, or until a toothpick inserted in center comes out clean. Cool 10 minutes, remove from pan and cool completely. Wrap in plastic wrap overnight before serving.
Join us and our Podcast host, Mark Borison, on a super safari every Wednesday as we explore the world of food, plus discuss people, art, culture, and more!