Ingredients
Equipment
Method
Prep and mix
- Preheat oven to 350°F and grease a 9x13-inch baking pan. The pan should be evenly coated so the cake releases cleanly.
- Whisk together all-purpose flour, sugar, baking soda, and salt. Mix until the dry ingredients are evenly combined in both color and texture.
- In a separate bowl, mix buttermilk, vegetable oil, eggs, and vanilla extract. Stir just until the mixture looks smooth and glossy.
- Pour wet ingredients into dry and stir until just combined, then fold in fresh rhubarb, diced. Stop stirring once you no longer see dry flour pockets.
- Spread batter into the prepared pan and smooth the top. Push the rhubarb down slightly so it’s packed throughout the sheet cake.
- Mix sugar and cinnamon and sprinkle evenly over the batter. Distribute the topping in a thin, even layer so every slice gets some crunch.
Bake and cool
- Bake at 350°F for 40-45 minutes until golden and a toothpick comes out clean. The center should set without wet batter clinging to the toothpick.
- Cool the cake for 30 minutes before serving. Let it rest until warm to room temperature so slices hold together.
Notes
For the cleanest slices, let the cake cool fully on the pan, then cut. Store covered in the refrigerator up to 4 days; it can be frozen up to 2 months (thaw overnight in the fridge). For a slightly lighter option, you can use low-fat buttermilk and reduce vegetable oil to 1/3 cup without changing the bake time.