Store in the refrigerator until ready to serve if using faux-tempered chocolate.
Preheat oven to 350 degrees. Spread pecans in a single layer on a rimmed baking sheet; toast until dark and fragrant, 12 to 14 minutes. Let cool completely, then coarsely chop.
Line a rimmed baking sheet with parchment. In a medium saucepan, combine butter, sugar, 1 tablespoon water, and salt. Bring to a boil, stirring until butter melts, then reduce heatto medium-high and continue cooking, swirling pan occasionally, until a candy thermometer registers 280 degrees. Reduce heat to medium and continue cooking until thermometer registers 298 degrees.
Remove from heat, stir in vanilla, and let stand until bubbles subside, about 30 seconds. Stir once, then pour mixture into center of prepared sheet, using a small circular motion (mixture will spread toward edges in an oval shape). Immediately sprinkle evenly with pecans. Let stand until hard and dry, about 1 hour.
Drizzle half of chocolate evenly over top (reserving remaining chocolate for another use). Let stand until hard and dry, about 2 hours. Break into small pieces and serve, or store between layers of parchment in an airtight container at room temperature up to 1 month.