Preheat the oven to 340F (170C). Line two baking sheets with parchment paper.
In a heatproof bowl, melt the chocolate with the oil, over a bain-marie.
In a large bowl, mix together the egg with both sugars. Add the buttermilk and vanilla, and mix to combine.
Add the melted chocolate and mix until incorporated.
Sift together the flour, cocoa powder, baking soda, and salt in a bowl.
Add half of the flour mixture and half of the hot coffee to the batter and mix until incorporated. Scrape down the sides of the bowl. Add the remaining flour mixture and the remaining half of the coffee and mix until completely combined.
Take a piping bag with a round ½ inch (1cm) tip and fill it with the cookie batter and pipe onto the baking sheets V-shaped cookies, they should be around 2-3 inches (7-8 cm) in diameter. Try to make them similar, so you can pair them later.
Bake one sheet at a time for 10 minutes each. Let them cool in the pan.