- With the rack in the middle position, preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper or a silicone mat.
- In a bowl, combine the flour, cocoa powder, baking soda and salt. Set aside.
- In a small bowl, dissolve the cornstarch in the water. Set aside.
- In another bowl, combine the brown sugar and oil with a whisk. Add the dry ingredients and the cornstarch mixture. Reserve 2 tbsp (30 ml) of the dark chocolate to garnish the cookies. With a spatula, fold the remaining chocolate in the dough.
- With a 2-tbsp (30 ml) ice cream scoop, shape the dough into balls. Place them on the baking sheet. Garnish with the reserved chocolate.
- Bake for about 10 minutes or until the cookies are firm on the outside but still soft in the centre. Let cool on the baking sheet.