Homemade Thin Mint Cookies

unsalted butter, softened to room temperature

granulated sugar

large Eggland's Best egg, at room temperature

pure vanilla extract

peppermint extract1

and 1/2 cups (188g) all-purpose flour (spoon & leveled)

unsweetened natural cocoa powder (or dutch process)

baking powder

salt

quality semi-sweet chocolate, coarsely chopped

canola or vegetable oil

peppermint extract1

Sifter (here's the one I own and love)

-inch-- or similar small size-- circle cookie cutter (I own this set, another option here and 2.5-inch option here)