Preheat your oven to 350F and spread the pecans out in a single layer. Bake 8 minutes or so, until nicely toasted. Keep your eye on them so that they don't burn.
Remove and let cool completely, then transfer to a food processor and process until well ground (but do not let them become butter). Set aside.
Reduce the oven heat to 325F and line two baking sheets with silicone mats (parchment can work but they can burn more easily).
In a large bowl, beat the butter with the sweeteners until well combined. Beat in the egg and the vanilla extract, then beat in the ground pecans, almond flour, baking soda, and salt.
Use a 1 tablespoon cookie scoop to scoop out onto the prepared baking sheets, leaving at least 2 inches between each cookie. (You can also use a regular spoon but you want only 1 tbsp of dough per cookie). You should get about 30 cookies.
Bake 5 minutes, then remove from the oven and press down with a flat bottomed glass to flatten them out. If your dough is sticking to the glass, cover the cookies with parchment before pressing down.
Return to the oven and bake another 10 minutes or so, until golden brown. Remove and let cool completely on the pan. Some oil may leach out during the baking process but it will re-absorb as they sit and cool.
In a heatproof bowl set over a pan of barely simmering water, combine the chocolate and butter. Stir until melted and smooth.
To dip cookies: Dip the cookies in the chocolate to about halfway up and hold above the melted chocolate to let the excess drain off. Lay on a waxed paper lined baking sheet. Sprinkle with additional chopped pecans, if desired. Refrigerate until set.
To make sandwich cookies: Spread about 2 tsp of the chocolate mixture on to the bottom of one cookie and top with another cookie. Refrigerate until set.
Storage tip: These cookies are best stored on the counter in a covered container. They will last 5 days or so.