Preheat your oven to 180°C/350°F, sprinkle the almond powder on a baking sheet and toast it for around 8 minutes. Keep an eye on it as it burns easily. Then set aside to cool.
Whisk together the flour, sifted cocoa powder, baking soda, baking powder and salt.
In a separate bowl, whisk together the oil, milk, sugars, cornstarch and add in the slightly cooled almond powder. Then line the baking sheet with parchment or a silicone mat.
Stir in the dry ingredients. Here you can opt to mix the chocolate pieces and walnuts into the dough instead of topping the cookies with them before baking.
With a 1-1½ tbsp scoop, portion the dough onto the prepared baking sheet and top with pieces of chocolate, chopped walnuts and flaky salt.
Bake for 10-12 minutes, then let them set on the baking sheet for 1-2 minutes befor transferring to a wire rack to cool completely.