Lightly butter the sides of 8-inch square pan. Cut an 8" by 12" piece of parchment paper to fit the bottom and up 2 of the 4 sides of that pan and set it in place. (The parchment extending the sides of the pan will later be used as handles to lift the fudge out once set.)
Place brown sugar, 3/4 cup butter and milk in medium pot set over medium heat. Heat and continually stir the mixture just until sugar and butter are melted. Increase the heat to medium-high, bring the mixture to a boil, and boil one minute.
Transfer the mixture to the bowl of your stand mixer. Add the icing sugar and vanilla to the pot and beat on low speed 1 minute. On medium speed, beat 5 minutes, or until mixture begins to hold its shape, but is still reasonably fluid and is warm to the touch (the fudge will set when cooled).
Mix in the pecans pieces. Spoon and evenly spread the fudge into pan. Cool to room temperature and then cover and refrigerate for 2 hours, or until firm.
When needed, let the fudge warm at room temperature about 1 hour, as that will soften it a bit and make it easier to unmould without crinkling on the surface. Now loosen the fudge from the sides of the pan with a paring knife, and then grab on to the parchment and lift out of the pan and on to a cutting board.
Cut the fudge into 4 equal quarters. Now cut each quarter into 16 small, but divine squares of fudge. If desired, decorate the top of each square of fudge with a pecan half, gently pressing it on to help it adhere.