1. Preheat oven to 175°C (350°F) and line a baking sheet with parchment paper.

2. In a mixing bowl, cream together butter, granulated sugar, and brown sugar until light and fluffy.

3. Add the egg and vanilla extract, mixing until well combined.

4. In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.

5. Gradually add the dry ingredients to the wet ingredients, alternating with the milk, mixing until fully combined.

6. Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them 5cm apart.

7. Bake for 8-10 minutes, or until the edges are set but the centers are still soft.

8. Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack.

9. While the cookies cool, prepare the icing: In a saucepan over medium heat, melt butter and stir in cocoa powder and milk.

10. Bring the mixture to a gentle simmer, then remove from heat and whisk in powdered sugar and vanilla extract until smooth.

11. Spoon the warm icing over each cookie and top with chopped pecans if desired.

12. Allow the icing to set before serving.