Preheat oven to 350F. Butter a 9″ round cake pan and line the bottom with parchment paper. (To do this, place your pan on a sheet of parchment and draw a circle around it. Then cut the circle about 1/3 inch inside the line.)
In the top of a double boiler over hot (not boiling) water, add the butter and 1 cup of the dark chocolate chips. Heat, stirring occasionally, until the mixture is completely melted. Pour into a large mixing bowl.
Whisk in the granulated sugar until combined. Whisk in the eggs one at a time, then the vanilla. Stir in the flour, salt, and espresso powder and stir until fully incorporated and the batter is smooth and has a bit of shine.
Transfer the batter into the prepared pan and bake for 26-30 minutes, or until a toothpick inserted in the center comes out clean.
Allow to cool fully, then slice into 12 “pie slices”. Heat your green candy melts (if using) according to package instructions (usually this will be microwave at 50% in short bursts of 30 seconds until desired consistency). Transfer the melted candy into a zip-loc baggie and snip off a tiny corner of the baggie with a sharp scissors. Drizzle green candy melts, or frosting, over slices to form the zig-zag Christmas tree design. Sprinkle with sprinkles before it dries. Insert lollypop stick, or candy canes, for the “trunk”
