Blend butter until smooth in a large bowl. Add egg and dry cookie mix and continue blending until a dough forms. Gather dough into a flat disc, wrap with plastic and freeze 20 minutes, until firm.
Preheat oven to 350 degrees and line a baking sheet with parchment. Remove dough from freezer and remove from plastic. Using your hands, flatten the dough onto the parchment paper in an oval shape, until approximately 1/4" thick. Bake for 25-30 minutes, or until the entire cookie begins to turn golden brown.
Remove from oven and cool completely on baking sheet. In a microwave safe bowl, melt the white chocolate chips. Heat in 30 second increments, stirring after each time, until smooth. Pour melted white chocolate over cooled cookie crust and spread with a spatula to evenly coat.
Cover with pretzel sticks, chocolate candies and sprinkles. Freeze for 10 minutes to set chocolate, then cut into strips.