Preheat the oven to 350 degrees F. Tear a sheet of parchment paper and place it in a 9" cast iron skillet that is fairly deep. My standard Lodge 9" skillet was perfect. No need to do anything fancier with the paper than place it in the skillet and fold a few edges into it so that it roughly sits in the pan with its corners hanging over the edges.
Make the blondies first: Stir together the melted butter and sugar. Stir in the vanilla and eggs. Once they are all combined, stir in the flour, salt, and baking soda.
Spread the blondie batter into the lined skillet, trying to keep as much of it as possible from getting caught in any wrinkles in the paper ( this is not as hard as it sounds, I promise. )
Baked at 350 for 25 minutes.
While the blondie crust is baking, prepare the pecan pie filling: Combine the maple syrup and melted butter in a large bowl. Stir in the sugar, bourbon, vanilla, and salt. Stir in the eggs until they are well combined. Stir in the pecan pieces.
When the blondes come out of the oven, let them rest for about 10 minutes, then pour the pecan pie filling on top and place the skillet back in the oven for 30 minutes.