Rhubarb-Buttermilk Muffins

1 1/2 cups brown sugar
1/4 cup salad oil
1 egg
2 tsp vanilla extract
1 cup buttermilk
1 1/2 cups finely diced rhubarb
1/2 cups pecan pieces
2 1/2 cups all-purpose flour
1 tsp baking powder
1 tsp baking soda
1/2 tsp salt

Topping:
1/3 cup sugar
1 1/2 tsp cinnamon
1 tbsp melted margarine

Preheat oven to 400 degrees. Grease 24 medium-sized muffin cups. Combine in large bowl: brown sugar, oil, egg, and vanilla. Beat until well mixed. Stir into mixture buttermilk, rhubarb, and pecans. In another bowl, sift together flour, baking powder, baking soda, and salt. Add this mixture all at once to rhubarb mixture and stir until all ingredients are moistened. Do not overmix. Fill prepared muffin pan 3/4 full with batter. Quickly combine topping ingredients and sprinkle on top of batter in each muffin cup.

Bake in preheated oven on center shelf 15 to 20 minutes.