Preheat the oven to 350℉/180℃. Line baking sheets with parchment paper.
In a large bowl, mix oat flour, cocoa powder, baking soda, salt, and instant coffee until well combined. Set aside.
Using a hand mixer or stand mixer fitted with a paddle attachment, cream together butter, brown sugar, and granulated sugar on high speed until pale and fluffy.
Scrape the sides of the bowl with a spatula. Add egg and vanilla. Beat the mixture until well combined.
Add the dry ingredients to the wet ingredients. Beat on low speed just until combined. Don't overmix.
Add chocolate chips, leaving a little bit for decoration. Mix with a spatula until well combined.
With a 1.6 inch/4 cm ice cream scoop (about 1.5 tablespoons), drop the dough on prepared baking sheets, leaving 2 inch apart.
Place some chocolate chips on top of each cookie to decorate.
Bake for 9-11 minutes.
Immediately after removing the cookies from the oven, sprinkle sea salt flakes on top of the cookies.
Let cookies cool on the pan for 5 minutes before transferring them to a cooling rack to cool completely.