Preheat the oven to 350°F. Fully line a 9x13 metal pan with parchment paper; set aside until ready to use.
In a large mixing bowl, beat room-temperature salted butter and vanilla extract with an electric mixer until fluffy. Then, beat in powdered sugar until well combined. Next, add the flour and mix until a soft dough forms.
Transfer the dough to the prepared pan and press it evenly into the bottom and about an inch up the sides. Prick all over with a fork to prevent bubbling. Bake in the 350°F preheated oven for 12 minutes. Remove the crust from the oven and allow it to cool for about 10 minutes before adding the filling.
While the crust is baking, prepare the filling. Start by melting unsalted butter in a large microwave-safe bowl in 30-second increments until fully melted. Then, whisk in both dark and light Karo syrup and vanilla extract.
Next, whisk in the dark and light brown sugars. Then, whisk in the heavy whipping cream and slightly beaten eggs.
In a small bowl, stir together flour, cinnamon, and Kosher salt until combined. Then, whisk the mixture into the filling. Stir in the toasted pecan pieces and chocolate chips. Then, ladle the filling over the crust.
Bake at 350°F for about 35 minutes, or until the center looks just set and not sloshing around. Remove from the oven and allow to cool for at least three hours before slicing into bars2.