Preheat the oven to 325°F and line two rimmed baking sheets with parchment paper.
In a large bowl, beat the butter and sweetener together until lightened and fluffy, about 2 minutes. Beat in the almond flour, coconut flour, vanilla extract, and salt until well combined. Stir in the chopped pecans.
Roll the dough into 1-inch balls and place a few inches apart on the prepared baking sheets. Flatten slightly with the palm of your hand.
Bake 5 minutes then remove from the oven and use a flat-bottomed glass to flatten again to about ¼ inch thick. Return to the oven and bake another 10 to 12 minutes, until the edges are golden brown.
Remove and let cool completely. Store on the counter for 4 days and in the refrigerator after that.