Set out butter and eggs to stand at room temperature for about 30 minutes. Line muffin cups with paper bake cups. Preheat oven to 350°F.
In a small bowl stir together brown sugar, pecans, and cinnamon. Set aside.
In a medium bowl stir together flour, baking powder, and salt.
In a large mixing cream the butter with an electric mixer on medium to high speed for one minute. Reduce speed to medium and gradually add in granulated sugar until combined, scraping sides of bowl occasionally. Beat on medium speed for 2 minutes more or until light and fluffy. Add eggs, one at a time, beating well after each addition. Add in flour mixture, vanilla, cinnamon and milk, beating on low speed after each addition just until combined (batter may look lumpy).
Spoon about 1 rounded tablespoon of batter into each prepared muffin cup. Sprinkle 1 teaspoon of the brown sugar mixture over batter in cups. Spoon remaining batter evenly over brown sugar mixture in cups. Sprinkle remaining brown sugar mixture over batter in cups.
Bake 20 minutes or until a toothpick inserted in centers comes out clean. Cool cupcakes in muffin cups on wire racks for 10 minutes. Remove cupcakes from muffin cups. Cool completely on wire racks.