Preheat oven to 325°F. Line a baking sheet with parchment paper or a silicone baking mat.
In a stand mixer fitted with a paddle attachment, or with a hand mixer, cream together the butter with both sugars on medium speed until light and fluffy, about 2-3 minutes.
With the mixer on low, slowly add in the eggs, one at a time, followed by the vanilla. Mix until combined, about 1 minute.
In a medium bowl sift together the flour, baking soda, baking powder and salt. With the mixer on low add dry ingredients to the wet in 2 batches and mix until incorporated.
Fold in the oats and pecans by hand with a silicone spatula or wooden spoon until fully incorporated. Wrap the bowl with plastic and place in the refrigerator for 30 minutes to allow the dough to firm up.
Using a small 1 1/2 tbsp. cookie or ice cream scoop, scoop the dough onto the prepared baking sheet about 1 inch apart. These cookies will spread and become very flat and lacy.
Bake on the middle rack, one tray at a time, for 8-11 minutes or until lightly golden, set and lacy. Let sit for 2-3 minutes before removing and letting cool fully on a cooling rack. Continue with remaining dough*.
Recipe Courtesy of Megan Mitchell
*You can roll extra cookie dough into 1 1/2-inch wide logs and wrap in parchment and freeze until needed