Rhubarb Chocolate Chip Muffins

2 3/4 cup all purpose flour
1 1/3 cup packed brown sugar
2 1/2 tsp baking powder
 1/2 tsp baking soda
1/2 tsp cinnamon
 1/4 tsp salt
 1 egg
1 cup buttermilk
1/2 cup vegetable oil
2 tsp vanilla
1 cup milk chocolate chips
 3/4 diced fresh or frozen rhubarb

TOPPING
1/2 cup chopped pecans
 1/3 cup packed brown sugar
 1/2 tsp cinnamon
1Tbl cold butter

 In a large bowl, combine the first six ingredients. in another bowl, whisk the egg, buttermilk, oil, and vanilla. Stir into dry ingredients just until moistened. Fold in chocolate chips and rhubarb. Fill greased muffin tins or paper lined muffin tins two-thirds full. In a small bowl, combine the pecans, brown sugar, and cinnamon. Cut in butter until mixture resembles coarse crumbs. Sprinkle over batter. Bake at 400 degrees for 20 to 25 minutes or until a toothpick comes out clean. Cool for five minutes, before removing from pans to wire racks. Yield 18 muffins.