Add pecans to a food processor and process until finely ground, being careful you don't over-blend or you'll end up with pecan butter!
Add pecan flour and almond flour to a skillet or pan, and toast over medium heat until golden and fragrant (3-6 minutes). Remove from pan aand set aside to cool completely (very important!). Whisk in the coconut flour, xanthan gum and salt, set aside.
Cream butter in a large bowl with an electric mixer, 2 minutes. Add in sweetener and continue to beat until light and fluffy (7-8 minutes). Add in vanilla extract and egg, beating until just combined.
With your mixer on low, add in half of your nut flour mixture- mixing until just incorporated. Mix in the rest. Wrap cookie dough with cling film (saran wrap) and refrigerate for at least an hour (and up to 3 days).
Preheat oven to 350°F/180°C and line a baking tray with parchment paper.
Divide dough into either 20 rounds. Place shaped cookie rounds on the prepared baking tray and place in the freezer for 15 minutes prior to baking.
Bake for 9-11 minutes. The cookies will be barely golden and still appear largely uncooked (worry not!). Sieve a touch of powdered sweetener with cinnamon on top immediately (it'll dissolve into the warm cookies).
Allow to cool completely before rolling in more powdered sweetener. Store in an airtight container for up to 1 week.