In a medium saucepan, combine butter, sugar, milk, and egg. Set over moderate heat and cook, stirring constantly, until the mixture comes to a full boil. Remove from heat and stir in the vanilla and salt. Add the graham cracker crumbs and pecans and stir until combined. Set aside and allow to cool for half an hour.

Line a small baking sheet with parchment paper. Place 6 of the graham crackers, face down, onto the baking sheet. Line them up to make a large rectangle about 10x7-inches. Two rows of three, making sure they're all touching each other.

Once the filling has cooled, add it by spoonfuls to the graham crackers. Carefully spread out the filling into an even layer, making sure that the graham crackers underneath do not move. Top with the remaining graham crackers, aligning them with the bottom pieces. Cover loosely with plastic wrap and chill for at least 4 hours or overnight.

Slice into 12 even squares, using the perforations already on the crackers as a guide. Return them to the baking sheet. Place the chocolate in a heat proof bowl and heat in the microwave in short 30 second bursts, stirring in between each, until completely melted and smooth. Dip the side of each sandwich cookie into the chocolate and return to the pan. Let the chocolate set before serving. Store in the fridge in an airtight container. Enjoy!