Instructions

1. Prepare the pan: Preheat the oven to 350°F (175°C). Grease and line a 9×5-inch loaf pan with parchment paper.
2. Mix the batter: Whisk together the flour, baking powder, baking soda, salt, and cinnamon. In another bowl, whisk the sugar, melted butter, eggs, buttermilk, and vanilla until smooth. Fold the dry ingredients into the wet ingredients, then gently stir in the diced rhubarb.
3. Create the swirl: Pour half the batter into the prepared loaf pan. Sprinkle with the brown sugar and cinnamon mixture, then add the remaining batter. Lightly swirl with a butter knife and sprinkle with the optional cinnamon sugar topping.
4. Bake: Bake for 55–65 minutes, or until a toothpick inserted into the center comes out clean. Tent loosely with foil during the last 15 minutes if the top browns too quickly.
5. Cool and serve: Let the bread cool in the pan for 15 minutes before transferring it to a wire rack. Slice once completely cooled and enjoy.