In a medium bowl, combine flour, cocoa powder, and salt. Mix well and set aside.

Using an electric mixer on medium-high speed, beat the softened butter and granulated sugar until light and fluffy, about 2 minutes.

Add the egg yolk, milk, and vanilla extract to the butter-sugar mixture, and mix until nicely incorporated.

Reduce the mixer speed to low and blend in the flour mixture until just combined. Cover the dough with plastic wrap and refrigerate for one hour.

Preheat your oven to 350 degrees Fahrenheit.

In a small bowl, whisk the egg whites until frothy. Place finely chopped pecans in another bowl.

After the dough has chilled, roll it into 1-inch balls.

Dip each dough ball into the egg whites, then roll them in chopped pecans.

Arrange the coated cookies about 2 inches apart on a lightly greased baking sheet.

Using a 1/2 teaspoon measuring spoon, gently press into the center of each dough ball to create an indentation.

Bake for 8-10 minutes, or until just set.

While cookies are baking, place the unwrapped caramels and heavy cream in a microwave-safe bowl. Microwave for one minute, stir, then continue in 20-30 second increments until melted.

When cookies come out of the oven, gently re-press the indentations and fill each with about 1/2 teaspoon of warm caramel.

Let cookies cool on the pan for about 10 minutes before transferring them to a wire rack.

If desired, melt the chocolate for drizzling; place it in a small zip-top bag, melt, and drizzle over the cookies.