Grease well a 12-cup muffin tin or line with paper cupcake liners.
In a bowl beat butter and sugar until smooth; add in buttermilk, egg and vanilla and mix well.
In another bowl combine flour, 1 teaspoon cinnamon, baking powder, baking soda and salt. Slowly beat the flour mixture into the bowl, mixing thoroughly.
In a small bowl, mix 1/2 teaspoon cinnamon with the brown sugar and pecans.
Fill muffin cups half way up with batter. Spoon in some brown sugar-pecan mixture, and repeat with a little more batter to fill the muffin cup up three-quarters. Sprinkle the top with the brown sugar-pecan mixture.
Bake 25 minutes. Makes 12 large muffins. They can be frozen after baking and completely cooled.