In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, salt, and cinnamon.
In a separate bowl, whisk together the egg, buttermilk, vegetable oil (or melted butter), and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir gently until just combined. Do not overmix—the batter will be slightly lumpy.
Gently fold in the diced rhubarb until evenly distributed throughout the batter.
Step 3: Make the Cinnamon Topping
In a small bowl, mix together the melted butter, brown sugar, flour, and cinnamon until crumbly. Set aside.
Step 4: Assemble and Bake
Divide the batter evenly among the 12 muffin cups, filling each about ¾ full.
Sprinkle the cinnamon topping generously over the batter in each muffin cup.
Bake for 18–22 minutes, or until a toothpick inserted into the center of a muffin comes out clean (a few crumbs are okay, but no wet batter).
Let the muffins cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.
Step 5: Serve and Enjoy
Serve the rhubarb muffins warm or at room temperature.
Pair with a pat of butter, a dollop of whipped cream, or enjoy them plain for a delightful treat.
Tips for Success
Rhubarb Prep: Trim off the leafy tops and ends of the rhubarb stalks before dicing. Rhubarb leaves are toxic, so discard them properly.
Sweetness Adjustment: If your rhubarb is particularly tart, you can increase the sugar in the muffin batter by 1–2 tablespoons to balance the flavor.
Storage: Store cooled muffins in an airtight container at room temperature for up to 2 days or in the refrigerator for up to 5 days. Reheat briefly in the microwave if desired.
Freezing: These muffins freeze beautifully! Wrap individually in plastic wrap and store in a freezer-safe bag for up to 3 months. Thaw at room temperature or reheat in the microwave.
