In a small bowl melt the chopped chocolate in the microwave in 30-second intervals. Set aside to cool for 5 minutes.
In a large mixing bowl combine the flour, cocoa powder, baking powder, and salt. Set aside.
In the bowl of a stand mixer, use the paddle attachment to beat the butter, brown sugar, and granulated sugar together for about 2 minutes, until combined and fluffy. Add in the eggs and vanilla and mix until just combined. Mix in the melted chocolate until just combined.
Add the dry ingredients to the wet and mix on medium-low until combined, being sure to scrape down the sides as needed.
Cover the dough and refrigerate for 2 hours.
Preheat the oven to 350° and line two baking sheets with parchment paper.
Scoop the dough into 18 1 ½ inch balls and place on the baking sheets, leaving 2 inches between the cookies. If the dough is too hard to scoop, let it sit for 15-20 minutes and try again. Bake for 10-12 minutes, until the edges are set and the center is still a bit gooey. Remove from the oven and let cool for 3 minutes on the sheet pan before transferring to a cooling rack. While the cookies are baking, prepare the german topping.
In a small saucepan whisk together the evaporated milk, sugar, egg yolk, and butter. Heat over medium-high heat until boiling and continue to cook for 10-15 minutes, until it is thickened and turning a golden brown. Whisk constantly to avoid curdling or burning.
Once thickened, remove from the heat and stir in the pecans, coconut, and vanilla. Set aside for 10-15 minutes to cool and finish thickening. If the sauce doesn’t seem to be setting up very thick, you can cook it for 5 or so minutes longer over medium-low heat, being sure to stir constantly.
Once the topping has cooled and the cookies are cooled, top each cookie with a scant tablespoon of the topping. Drizzle the cookies with melted chocolate. Let sit for 30 minutes or so, so the german topping is fully set up before serving.