Preheat oven to 350℉.
In a medium mixing bowl, whisk together the flour, baking soda, salt and cinnamon. Set aside.
In a medium skillet, melt 12 tablespoons of butter over medium heat, stirring frequently.
Once the butter is melted, continue to stir until it develops a nutty aroma and turns a golden brown color.
Remove from heat and immediately stir in the remaining 4 tablespoons of butter until melted. Allow the butter to cool for 5 minutes.
Stir in the brown sugar, maple syrup, vanilla, and sourdough starter. Stir in the eggs last so they do not cook.
Pour the wet ingredients into the dry ingredients and stir until mostly combined.
Stir in the chopped pecans and oats until completely incorporated.
Line a baking sheet with parchment paper. Use a spoon to roll balls of cookie dough measuring about 1¼ inches in diameter.
Place the cookie dough balls on the baking sheet, spacing 2 inches apart from one another.
Bake for 12-14 minutes. The edges should be golden but the centers should be slightly gooey when done. Do not over-bake or the cookies will be dry.
Allow the cookies to cool 5 minutes in the pan, then transfer to a wire cooling rack to cool completely.