Step 1: Preheat your oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease it well. This higher initial temperature helps the muffins rise quickly and form a beautiful dome.
Step 2: Dice your fresh rhubarb into small, 1/2-inch pieces. If using frozen, thaw and drain thoroughly. Set aside.
Step 3: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Make sure these are well combined to ensure even leavening throughout your rhubarb muffins.
Step 4: In a separate medium bowl, whisk together the buttermilk, melted unsalted butter (cooled slightly), large egg, and vanilla extract until smooth. Ensure the butter isn’t too hot, or it might cook the egg.
Step 5: Pour the wet ingredients into the dry ingredients. Using a rubber spatula, gently fold until just combined. A few lumps are perfectly fine and even desirable! The key here is not to overmix, as overmixing develops the gluten in the flour, leading to tough, chewy muffins. This is a crucial step for tender rhubarb muffins.
Step 6: Gently fold in the diced rhubarb until just distributed. Again, avoid overmixing. You want the rhubarb to be integrated, but don’t beat the batter.
Step 7: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full. For an extra touch, you can sprinkle a little extra granulated sugar on top of each muffin before baking for a sparkling, slightly crisp crust.
Step 8: Bake for 5 minutes at 400°F (200°C), then reduce the oven temperature to 375°F (190°C) and continue to bake for another 15-20 minutes, or until a wooden skewer inserted into the center of a muffin comes out clean. The initial high heat helps create that beautiful domed top.
Step 9: Remove the muffin tin from the oven and let the muffins cool in the tin for 5-10 minutes. Then, transfer them to a wire rack to cool completely. Allowing them to cool slightly in the tin prevents them from sticking and helps them hold their shape. This rhubarb muffins recipe tastes best when fresh and slightly warm!