Preheat the oven to 350℉.
In a large mixing bowl, cream together the butter and granulated sugar until smooth and fluffy.
Add the egg, oil, and vanilla extract and beat until well incorporated.
In a separate bowl, sift together the flour, both cocoa powders, baking powder, and powdered sugar. Add to the wet mixture and beat until just combined.
Stir in the coconut and mix until a soft dough forms.
Turn the dough out onto a floured surface and form into a ball. Place a sheet of plastic wrap over the dough and roll it out to about ¼ inch thickness.
Use a fork to gently scrape the surface of the dough in multiple directions to create a rough texture.
Cut shapes with an oval cookie cutter and transfer to a greased or parchment-lined baking sheet.
Bake for 15–17 minutes. Remove from the oven and let cool on the tray for 10 minutes before transferring to a wire rack to cool completely.
Once cookies are completely cool, place the milk chocolate chips in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each, until fully melted.
Let the chocolate cool for about 3 minutes, then spoon a small amount onto the flat side of one cookie. Top with another cookie and gently press to sandwich, letting the chocolate ooze slightly.
Place sandwiched cookies back on the rack and let the chocolate set completely before serving.