Preheat the oven to 350. Line 2 large cookie sheets with parchment paper.
In a large bowl stir together the flour, sugars, cocoa powder, baking soda, and salt.
Add the egg, vanilla, and butter. Mix until smooth.
Scoop 18 cookies, rolling each in powdered sugar before placing them on the prepared baking sheets.
Bake for 10-12 minutes, until barely set. Press down while warm so they are flat across the tops.
Buttercream
Stir together the butter and powdered sugar. Add the extract. Add milk, a few drops at a time, until a spreadable consistency.
Ganache
Put the chocolate chips and heavy cream in a small microwave-safe bowl. Microwave for 20 seconds. Stir. Repeat until 75% melted. Stir until all the chips melt.