Preheat oven to 350 degrees F (175 degrees C). Grease a 5x9-inch loaf pan. 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.
Our Rhubarb Bread recipe uses buttermilk which is an ingredient that we don’t always have in our refrigerator. Do not fret. There’s an easy remedy to not keeping buttermilk on hand. Can I make buttermilk?
In a large bowl, combine the six ingredients. In another bowl, whisk the egg, buttermilk, oil and vanilla. Stir into dry ingredients just until moistened. Fold in rhubarb. Fill paper-lined muffin cups two-thirds full. Bake at 350° for 22-25 minutes or until a toothpick comes out clean. Cool for 5 minutes before removing from pans to wire racks.
In a large mixing bowl or in the bowl of a stand mixer on low, mix brown sugar, oil, eggs and buttermilk, until smooth. Add in all purpose flour, vanilla extract, salt and baking soda, just until combined, scrape the sides of bowl if needed. Fold in diced rhubarb and chopped walnuts if desired. Pour into prepared pans, about ⅔ full.