Using a stand mixer, beat the butter and sugars together until light and fluffy (a few minutes).  Add in the egg and vanilla and beat until combined.

Add in flour, baking soda, and salt.  Beat until combined.  Do not over mix, just until combined.  Stir in the chopped pecans.

Cover the dough and refrigerate for 30 minutes.

Preheat oven to 350 degrees.

Shape the pecan cookie dough into 1 inch balls or 2 inch balls and place a few inches apart on a parchment lined cookie sheet.  Bake 10 minutes or until the cookies are set, and lightly browned on the edges.  Cool cookies before frosting.

Combine dark brown sugar and milk in a small pot over medium heat and bring to a boil.  Boil for about 3-4 minutes, stirring constantly.  

Remove from heat and stir in butter.  

Once butter is melted and incorporated, stir in 1 ½ cups of the sifted powdered sugar with a whisk.  If frosting is too thin, add in another ½ cup or so of the powdered sugar.  (We used all 2 cups of the powdered sugar.)  

Frost each cookie with about 1 tablespoon of frosting and top with a pecan or chopped pecans.  Let the frosting set before serving.