Whisk buckwheat flour, corn starch, tapioca starch, cocoa powder, baking soda, and salt in a medium bowl.
In a large bowl beat softened butter and sugars until creamy. You can use an electric mixer or a hand whisk.
Stir in the egg, and vanilla and mix well. Add buttermilk and mix until well incorporated.
Add dry ingredients, little by little, and mix well until you get homogeneous cookie dough. The dough is a bit sticky.
Finally, add the red food coloring and mix until the color has spread throughout the dough.
Place the dough covered in the fridge for at least 1 hour.
Preheat oven to 350ºF. Line baking sheets with parchment paper or silicone mats.
Drop large cookie dough balls on the prepared sheets, spacing them an inch or so.
Use your fingers to gently press down on the balls, flatten them slightly, and place the chocolate chunks on the surface of the cookies.
Bake for 10 minutes or until golden brown.
Let cool for at least 10 minutes before removing.
Cookies can be stored in an airtight container at room temperature for up to 5 days.