In a food processor, combine the all-purpose flour, cream cheese, and butter. Pulse until a crumble comes together, then transfer to a sheet of plastic wrap. Pull the crumbs together and wrap with plastic wrap, keeping your pie crust layer about an inch in thickness. Refrigerate for an hour.
Preheat your oven to 350 degrees F (175 degrees C). Remove refrigerated pie crust dough and cover the bottom of a parchment paper lined lasagna baking dish (I used a 15x9 pan). Push into all of the corners and cover the entire bottom, until you have an even layer covering the bottom of the pan.
Bake the pie crust layer at 350 degrees F (175 degrees C) for 20 minutes. While the crust layer is baking, start combining the filling ingredients.
Combine the first 1 cup portion of semi-sweet chocolate chips with the light corn syrup. Microwave in 30 second increments until the chocolate chips are melted (about 1 minute) and combined with the corn syrup. Allow to cool slightly before adding the beaten eggs (so the eggs don't cook!).
Once the melted chocolate and corn syrup are cooled, add the beaten eggs, light brown sugar and vanilla. Stir to combine, then stir in the first 2 cup portion of the pecan halves. Pour into baking pan over the partially baked cream cheese pie crust layer.
Bake at 350 degrees F (175 degrees C) for 35 minutes. Remove from the oven and allow to cool to room temperature. Refrigerate, if desired, before adding the final topping ingredients (I usually do this, and take the chocolate pecan slab pie bars to a gathering the next day).
Add the toppings: melt about 2/3 of the remaining 1 cup portion of the semi-sweet chocolate chips with 1 Tbsp of butter in 30 second increments in the microwave (about 1 minute). Drizzle the melted chocolate using a spoon, in a criss-cross pattern over the slab pie bars.
Crush the remaining pecans in a ziploc baggie, using a meat tenderizer or rolling pin. Spread over the top of the slab pie bars along with the remaining semi-sweet chocolate chips. I usually add some of the crushed pecans and chocolate chips and continue to drizzle more of the chocolate until all of the toppings are used.
Refrigerate to chill completely before slicing and serving, if desired. I cut into 5x6 rows for a total of 30 bars from my 15x9 baking pan.