01 -
Preheat oven to 325°F (163°C). Grease two 8×4-inch loaf pans or line them with parchment paper.
02 -
In a large bowl, whisk together brown sugar, vegetable oil, egg, buttermilk, and vanilla extract until smooth.
03 -
In a separate bowl, stir together all-purpose flour, baking soda, and salt.
04 -
Gradually add dry ingredients to the wet mixture, stirring until just combined. Avoid overmixing.
05 -
Gently fold in diced rhubarb and chopped walnuts until evenly distributed throughout the batter.
06 -
Divide the batter evenly between the prepared loaf pans, smoothing the tops.
07 -
Combine granulated sugar and cinnamon, then sprinkle the mixture evenly over both loaves.
08 -
Bake for 55 to 60 minutes, or until a toothpick inserted into the center comes out clean.
09 -
Let loaves cool in pans for 10 minutes, then transfer to a wire rack to cool completely before slicing.