In a large bowl combine flour, cornstarch, salt, cinnamon, and baking soda; whisk well to combine then set aside until needed.
In a small saucepan, over medium heat, melt the butter. Continue to cook the butter swirling the pan occasionally. Keep a close eye on it. The top of the butter should become foamy and you should hear tiny popping noises. The butter should develop into a rich amber color, with tiny brown bits at the bottom. It will have a rich nutty aroma. Once the butter reaches this stage, remove from the heat immediately and pour into a large mixing bowl.
Add both sugars into the mixing bowl and using the hand mixer at low speed, mix well to combine.
Beat in eggs and egg yolk, one at a time, beating until eggs are just combined.
Using a rubber spatula, fold in the flour, stirring until just combined.
Fold in the buttered pecans.
Cover the bowl and refrigerate for 4 hours.