Preheat oven to 450°F. Line a half sheet pan with nonstick aluminum foil and set aside until ready to use.
Place room temperature butter in a large bowl and beat on medium speed with an electric hand mixer for two minutes until creamy.
Next, add the light and dark brown sugars and beat for about two minutes until creamy.
Then, add both Karo syrups and beat until the mixture is smooth.
Next, add all six eggs and the vanilla extract and beat until everything is well incorporated. Use a rubber spatula to scrape down the bowl then mix it one last time to make sure everything was well incorporated.
Place both frozen pie crusts on the pan and fill each one with 1 ½ cups of toasted pecans.
Carefully ladle the filling over the toasted pecans, making sure not to overfill the pie shells. Please note, you will have a little bit of filling left over. If you do not, then you have overfilled your pie crusts.
Bake at 450°F for 10 minutes. Without opening the oven, reduce the temperature to 350°F and bake for an additional 50 minutes. The filling should be set at the edges with only a slight jiggle in the center; it will firm further as it cools.
Remove the pan from the oven and place on a wire rack. Leave the pies on the baking sheet until the pan is cool to the touch, then remove the pies from the pan and let them cool to room temperature on the wire rack. Once the pies have cooled, place each one in a gallon-size Ziploc freezer bag and place in the refrigerator overnight.2