Line an 8-inch square pan with non-stick foil or parchment paper.

In a mixing bowl, toss together the pecans, graham cracker crumbs, marshmallows, ½ cup of the powdered sugar and 2 tablespoons of the milk. Set aside.

In a small saucepan, combine the remaining ½ cup milk, chocolate chips, and butter. Heat over low, stirring constantly, until the chocolate and butter melt and the mixture is smooth. Pour only half of the chocolate mixture over the graham cracker mixture and stir until blended. Spoon into pan and press down evenly.

Add the remaining powdered sugar to the chocolate mixture in the saucepan and stir in until mixed.

Using a rubber spatula, scrape the chocolate mixture over the mixture in the pan. Cover and chill until chocolate is set.

Grasp foil, lift from pan and set on a cutting board. Trim edges and cut into 16 squares.