Preheat the oven to 375°F and have ready a cookie sheet lined with either parchment paper or a silicone baking mat.
In a medium-sized mixing bowl, whisk together flour, cocoa powder, baking powder, and sea salt. Set aside until ready to use.
Add the butter and chocolate chips to a microwave-safe bowl. Microwave at 30-second increments, stirring after each stint in the microwave until melted. Set aside.
Add the granulated sugar, eggs, peppermint and vanilla extract to the bowl of a stand mixer fitted with a paddle attachment. If you do not have a stand mixer, use a large mixing bowl and a handheld mixer. Mix on medium-high speed, until the mixture has lightened in color and almost doubled in volume. This should take at least 3 minutes.
Stream in the melted butter and chocolate and mix on low to combine.
Add the dry ingredients and mix just until combined.
Scoop heaping tablespoons of the cookie dough on to the cookie sheet, spacing them about 1 ½-2" apart, and press down slightly to flatten. Bake for 10 minutes and set aside to cool on the pan.
For the Peppermint Frosting
In the clean bowl of a stand mixer fitted with a paddle attachment, combine the butter and powdered sugar. If you do not have a stand mixer, use a large mixing bowl and a handheld mixer. Begin mixing on low speed, until most of the powdered sugar is mixed in, then increase the speed to medium-high. Mix until well-combined and fluffy.
Once the cookies have completely cooled, add a spoonful of icing to the top of each one and spread across the top using an offset spatula. Sprinkle with crushed peppermint candies, serve and enjoy!