Whisk together the flour, cocoa powder, and salt in one bowl, then beat the butter and sugar in a separate bowl for 2 to 3 minutes before mixing in the egg yolk, milk, and vanilla. The butter and sugar should look lighter in color and fluffy.

Add the dry mixture to the wet mixture and stir just until the dough comes together. Stop as soon as no dry streaks remain.

Cover and chill the dough in the refrigerator for 1 hour. After chilling, the dough should feel firm, cool, and easy to roll.

Heat the oven to 350 °F and line a baking sheet with parchment paper.

Lightly whisk the egg white in a bowl until frothy and place the finely chopped pecans in a second shallow bowl, then roll the dough into 20 small balls.

Dip each dough ball in the frothy egg white, roll and press it in the pecans, and arrange the coated balls on the prepared baking sheet.

Use the back of a small measuring spoon to press an indentation into the center of each ball. Make the well deep enough to hold caramel, but avoid pressing all the way through.

Bake for about 10 to 12 minutes, then remove the cookies and gently press the centers again with a small spoon while they’re still warm. The edges will look set and dry, but the center may still seem slightly underbaked.

Combine the caramel bits and water in a microwave-safe bowl and heat in 30-second bursts, stirring after each one, until melted, about 1 to 2 minutes total. The caramel should be smooth and spoonable.

Spoon small amounts of caramel into each indentation, then melt the semi-sweet chocolate and drizzle it over the tops if you like.