Combine dry ingredients in a medium sized bowl: flour, cocoa powder, espresso powder cornstarch, baking powder, and salt. Whisk and set aside.
In a small saucepan over medium-low heat, melt the chocolate chips and butter. Stir just until ingredients are melted and be careful to watch so chocolate doesn't burn. Remove from heat, stir in vanilla and peppermint extracts and cool.
Using a stand-mixer fitted with the whisk attachment, whisk the eggs and sugars for 3-4 minutes or until thick and pale in color.
Using a rubber spatula, stir in the cooled chocolate/butter mixture until well combined.
Add in the flour mixture and fold until combined, avoid over-mixing. Dough will look shiny.
Chill cookie dough in fridge for at least 10 minutes so batter can thicken and look more like cookie dough. (Chilling the dough will also help the cookies bake up thicker & help prevent spreading). Preheat oven to 350°F while dough chills.
Scoop batter using a cookie scoop so cookies come out even in size and place on a baking sheet or cookie sheet lined with parchment paper or a silicone baking mat.
Bake for 10-12 minutes. (Will make ~10 cookies, depending on size scoop you use).
Allow to cool on cookie sheet for 5 minutes, then transfer to wire rack to cool completely.
Melt white chocolate chips and coconut oil in a microwavable safe bowl in 30 seconds increments, stirring in between, until smooth.
Dip one side of the baked cookies into the white chocolate and add crushed peppermint candies and a sprinkle of flaky sea salt (optional).