Pulse 3/4 cup of the pecans in a food processor until finely ground; transfer to a medium bowl. Finely chop the remaining 1/2 cup pecans and set aside.
Add the flour, cinnamon, nutmeg and salt to the bowl with the ground pecans and whisk to combine. Set aside.
Cream together the coconut oil, sugar, sweet potato puree and vanilla in a stand mixer fitted with the paddle attachment on medium speed, scraping down the sides of the bowl with a silicone spatula to incorporate all of the ingredients, until no lumps remain, 2 to 3 minutes. Add the flour mixture and mix on low speed just until combined, scraping down the sides of the bowl as needed, about 1 minute. The dough will begin to pull together into a ball on the paddle.
Transfer the dough to a 2-foot-long piece of wax or parchment paper. Form the dough into a log roughly 2 inches wide. Fold the paper over the top of the log and roll up tightly, squeezing outwards from the center to push the dough into a longer log, about 15 inches long and 2 inches wide. Open the paper and sprinkle the top of the log with the reserved chopped pecans. Roll the log back and forth in the pecans, pressing down gently to adhere, until the log is completely coated. Roll the log back up tightly in the paper and twist the ends to seal. Refrigerate until the dough is firm to the touch, about 1 hour.
Position oven racks in the top and bottom thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment.
Slice the dough into 1/2-inch-thick discs with a chef's knife. Put the discs on the prepared baking sheets 2 inches apart. Bake, rotating the baking sheets from top to bottom and front to back halfway through, until the cookies are lightly golden, 18 to 20 minutes. Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a cooling rack to cool completely. Store in an airtight container for up to 3 days.
When measuring flour, we spoon into a dry measuring cup and level off excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)