Preheat the oven to 350°F.
Spread pecans out on a baking sheet and roast for 8 minutes. Let cool. Turn oven off.
Add the pecans to a food processor and pulse until tiny pieces form. Set aside ¼ cup of pecans pieces.
Add ¼ cup of flour to the food processor with the remaining pecans and blend until the pecans have a flour-like texture.
In a stand mixer fitted with a paddle attachment, cream together the butter and sugar for 2 minutes.
Add the vanilla, baking powder, and salt to the butter mixture and mix, scraping down the sides of the bowl as needed.
Add the remaining flour and the nut mixture and beat for 1 more minute.
Shape the dough into a log on parchment paper and chill in the refrigerator for at least 4 hours. The log should be 2 inches in diameter and about 18 inches in length. The dough is very soft so I recommend using parchment paper to help you roll and shape it.
After chilling, preheat the oven to 350°F and line a cookie sheet with parchment paper.
Remove from the refrigerator and roll the dough log in the reserved pecan pieces.
Slice the dough into ½-inch thick pieces and place 1 inch apart on the prepared cookie sheet. If your dough slices aren’t perfectly round, you can use your fingers to gently reshape them.
Bake for 10 to 12 minutes.