Preheat the oven to 400°F (200°C). Place the oven grate in the middle of the oven.
Grease or line an 18-cup muffin pan with paper liners. Set aside for now.
In a medium mixing bowl, sift or whisk together flour, baking powder, baking soda, salt and cinnamon. Set aside.
In a large bowl, whisk together the brown sugar with the oil.
To this, add a lightly beaten egg, the buttermilk and the vanilla extract. Whisk to combine properly together.
Add 1¼ cups of chopped rhubarb to the liquid ingredients and combine.
Add dry ingredients to the wet ingredients and combine with a wooden or rubber spoon. Do not over-mix.
Fill muffin liners ¾ full.
Divide the leftover rhubarb (¼ cup) evenly on the top of each muffin.
As an optional step, sprinkle with a combination of turbinado sugar and ground cinnamon.
Bake for 18-22 minutes or until the top bounces back when lightly touched.
Remove from heat. Gently lift out the freshly baked rhubarb muffins and transfer them to a wire rack to cool off.
Use room temperature ingredients to combine the wet ingredients properly.
Preheat your oven for at least 20 minutes before baking.
Whisking the dry ingredients together is important to distribute the leavening agents properly. This prevents large air tunnels in the finished product.
To avoid soggy muffins, cool them for only 1-2 minutes in the tin before removing and transferring to a wire rack to cool completely.
Sprinkling turbinado sugar over the top of the muffins before baking ensures glistening, crispy muffin tops. This is optional.
These muffins are best consumed the day they are made. The crispy top softens the following day.
Using frozen rhubarb: If using frozen rhubarb, thaw and drain first.Freezing muffins: Muffins freeze well for up to one month. Wrap completely cool muffins individually in plastic wrap and place them in a freezer bag or container. When ready to consume, simply thaw overnight at room temperature and if desired heat up in the oven. Please keep in mind that the nutritional information provided below is just a rough estimate and variations can occur depending on the specific ingredients used.