Farmer's Market Fresh Rhubarb Muffins

I made these Saturday after returning from the farmer's market with fresh Valentine Rhubarb.  The farmer told me this type is called "valentine" because it is so vibrantly red. 

Muffins:
2 1/2 cups flour
1 teaspoon baking soda
1 teaspoon baking powder
1/2 teaspoon salt
1 1/4 cups brown sugar
1/2 cup vegetable oil
1 egg
1 teaspoon vanilla extract
1 cup buttermilk
2 cups diced fresh rhubarb
1/2 cup chopped pecans
Topping:
1 tablespoon melted butter
1/3 cup white sugar
1 teaspoon ground cinnamon

Preheat the oven to 350 degrees.  Line two muffin pans with paper cups.

Beat the brown sugar, oil, egg, vanilla and buttermilk with an electric mixer until smooth.  Add the dry ingredients and mix by hand just until blended.  Stir in the rhubarb and the pecans.

Spoon the batter into the cups, filling almost to the top.  In a small bowl, stir together the melted butter, white sugar and cinnamon, sprinkle about 1 teaspoon of this mixture on top of each muffin. 

Bake for about 25 minutes.