For filling, in medium saucepan combine 3/4 cup butter, granulated sugar, 1/4 cup milk, and egg. Stirring constantly, cook over medium heat until mixture comes to full boil. Remove from heat. Stir in pecans and crumbs. Cool 30 minutes.
Meanwhile, place 6 of the graham cracker rectangles, side by side, on a foil-lined baking sheet to make a rectangle about 10x7 inches in size. Spoon filling in small mounds onto graham cracker rectangles. Carefully spread to an even layer being careful not to move crackers. Place remaining cracker rectangles on top to match up with bottom rectangles. Lightly cover bars with plastic wrap. Chill in the refrigerator at least 4 hours or until filling is firm. Cut into bars.
In small bowl beat 1 tablespoon butter with whisk or electric mixer until smooth. Gradually whisk in powdered sugar and enough milk to make a thick drizzling consistency. Drizzle over bars. Let stand until set. Makes 24 bars.