Preheat oven to 350°. Spread pecans on a rimmed baking sheet and toast, stirring every 5 minutes, until toasty smelling and light golden inside, 8 to 10 minutes. Let cool, then coarsely chop.
In the bowl of a stand mixer fitted with the whisk attachment or in a large bowl using a hand mixer, on medium-high speed, cream butter and granulated sugar until fluffy and pale. Beat in vanilla and salt, then fold in flour with a rubber spatula until only a few dry streaks remain. Add pecans and fold to combine.
Divide dough in half (about 350 g. per half). Arrange each half in the center of a square piece of plastic wrap. Using plastic, form dough into an 8" log. Twist ends of plastic wrap to seal and refrigerate until firm, at least 1 hour.
Preheat oven to 350° and line 2 baking sheets with parchment paper. Remove 1 dough log from refrigerator and unwrap. Place decorative sugar, if using, in a small flat container. Roll dough in decorative sugar, pressing to help sugar adhere to sides of log.
Using a sharp knife, slice dough log into 1/2" coins; arrange on prepared baking sheets, spacing 1" apart. Bake until golden brown around the edges, 12 to 15 minutes. Let cool 2 minutes on baking sheet, then transfer to a wire rack and let cool completely. Store in an airtight container. Repeat with remaining dough.
Make Ahead: Dough can be made 1 week ahead; keep wrapped in plastic in refrigerator, or freeze up to 1 month.