"Great way to use summer rhubarb."
1. Preheat oven to 350 degrees F (175 degrees C). Grease a 5x9-inch loaf pan. 2. Mix brown sugar, vegetable oil, egg, buttermilk, flour, baking soda, salt, and rhubarb, in exact order and stirring after each addition, together in a bowl until batter is just combined; pour into the prepared pan. 3. Combine white sugar, butter, and cinnamon together in a bowl until crumbly; lightly press onto batter. 4. Bake in the preheated oven until a toothpick inserted in the center of the bread comes out clean, about 1 hour.