Preheat oven to 350° F.

In a medium bowl combine flour, cocoa powder,baking soda and salt and whisk to combine with a wire whisk.

Set aside.

In the bowl of a mixer cream the butter and sugars.

Add eggs and vanilla extract and mix to combine well.

Add the flour & cocoa mixture a little at a time, scraping the sides of the bowl as needed, until all the dry ingredients have been incorporated.

Mix in chocolate chunks by hand with a wooden spoon or spatula.

Using a large cookie scoop (I used a 3 tablespoon sized scoop), scoop out 6 balls of dough on a rimmed cookie sheet and bake 12 minutes.

Let cookies cool on pan for 5 minutes and then transfer to a wire cooling rack till completely cool.

Continue with the remaining cookie dough.

In the bowl of a stand mixer beat the softened butter till creamy.

Add in the powdered sugar a little at a time until it has all been mixed in, adding a splash or two of milk as needed to get to the desired consistency.

Add peppermint oil to your desired minty-ness is desired (I like it minty so used 10 drops of peppermint oil).

Add food coloring if desired.

Assemble cookie by spreading or piping icing between two cookies.