On a sheet pan, add 1 1/2 cups pecan halves and bake for 10 minutes until they are toasted and appear slightly darker. Once cool enough to handle, give a rough chop and set aside.
In a large bowl, whisk together the brown sugar and maple syrup until incorporated. Add eggs, one at a time, whisking to make sure each egg is blended before adding another.
Next, add the vanilla, sea salt, cinnamon and flour, whisking out any lumps. Add the butter and continue whisking to incorporate. With a rubber spatula, fold in the chopped pecans.
After 10 minutes, reduce the oven temperature to 350 degrees. The pie will rise and puff up all the way to the center. The top will crack, but will quickly settle down after it cools.