Be sure to have everything ready ahead of time and work quickly, because this icing becomes firm quickly.
Set a wire rack over a cookie sheet and set aside.
Sift 1 cup confectioners' sugar into a medium bowl. Place about 20 pecan halves (one for each cookie) in a small bowl. In a small sauce pan bring 1 cup packed light brown sugar, 6 tablespoons heavy cream, 4 tablespoons unsalted butter, and a pinch of salt to a boil over a medium-high heat, stirring frequently. Reduce the heat and simmer for 3 minutes, stirring constantly. Remove from heat stir in 1 teaspoon vanilla extract. Pour the brown sugar mixture slowly into the confectioners' sugar while stirring, and continue to stir until smooth. When cooled just enough to touch, dip a cookie into the icing, then place on the wire rack and top with a pecan half.