Preheat the oven to 375 degrees F and line a cookie sheet with parchment paper.
Add the butter, brown sugar, and granulated sugar to a large bowl. Using a hand mixer, beat on medium until light and fluffy, about 3 mins.
Add the eggs and vanilla. Beat until combined.
Add the flour, cocoa powder, baking soda, and salt. Beat until the flour is worked into the cookie dough.
Using a small cookie scoop, scoop the cookie dough and place it on the prepared cookie sheet 2 inches apart. I do 3 rows of 4.
Place in the oven and bake for 12 - 14 minutes until done. The edges will be set and the center will be a matte color when they're done.
Let cool on the baking sheets for 5 to 10 minutes before transferring to a cooling rack or paper towel to cool completely. While the cookies are cooling make the topping.
Topping
Add the evaporated milk, granulated sugar, egg yolks, and butter to a medium saucepan. Cook on medium heat for 10-12 minutes stirring frequently so the egg yolks don't become scrambled eggs. Once the sauce thickens remove it from heat.
Stir in vanilla, coconut, and pecans. Set aside and let cool before adding to the cookies.
Scoop a tablespoon of filling on top of each cookie just before serving.
For just the cookies, place them in an airtight container at room temperature.
For the cookies with topping, place in an airtight container in the fridge.