Preheat oven to 375°F (190°C). Grease a 12-cup muffin tin or line with paper liners.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, beat together the butter and sugars until light and fluffy. Add the eggs, one at a time, beating well after each addition. Add the vanilla extract.
Add the dry ingredients to the wet ingredients and mix until just combined. Stir in the rhubarb and walnuts, if using.
Divide the batter evenly among the prepared muffin cups. Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the tin for 10 minutes before transferring to a wire rack to cool completely.
Interesting Facts
Rhubarb is a type of vegetable, not a fruit.
Rhubarb was cultivated in China as early as 2700 BC.
Rhubarb is a good source of Vitamin K and Vitamin C.