Toast the pecans at 350°F (175°C) for 8–10 minutes, until fragrant and slightly darker. Cool them completely, then chop finely.

Cream the softened butter and sugar until smooth. Beat in the egg yolk and vanilla.

Whisk together the flour, cocoa powder, and salt. Add the dry ingredients to the butter mixture and mix just until combined, then fold in the toasted pecans.

Shape the dough into a log, wrap it securely, and chill for 30–60 minutes, or until firm.

Slice the chilled log into rounds about 1/4 inch (6 mm) thick. Arrange the rounds on parchment-lined baking sheets.

Bake at 350°F (175°C) for 10–14 minutes, until the edges are set. Cool briefly on the baking sheet before transferring the cookies to a wire rack.

For the caramel leaves, boil the sugar, water, and optional syrup without stirring until the syrup reaches a deep amber color. Spoon or drizzle small leaf shapes onto a silicone mat or parchment and let them harden for 15–20 minutes.

Attach the caramel leaves to completely cooled cookies shortly before serving. Handle the hot caramel carefully, and keep the finished garnish away from humidity.