In a big mixing bowl, add the flour, baking powder, and cocoa powder. Mix with a whisk until combined and set aside.
Into a big mixing bowl, or in a bowl of a stand mixer, add the room temperature butter, brown sugar, and granulated sugar, and cream it for 2-3 minutes or until it’s creamy and light in color.
Add the egg, vanilla extract, milk, and salt. Mix until well combined.
Sift half of the dry ingredients and mix until almost combined. Add the other half of the dry ingredients. Mix until the mixture is just combined and you cant see pockets of flour.
Cover the dough bowl with plastic wrap and let the dough rest in the fridge for at least an hour. We let the dough rest in the fridge overnight but it’s not a must.
Using an ice cream scooper, scoop out balls and roll them into balls. Using your thumb or a teaspoon, make indents to each cookie.
Bake the cookies in a 180c (350f) preheated oven for 10 minutes. Don’t overbake these cookies so they will stay soft!
We bake these cookies without the ganache, unlike other thumbprint cookies recipe that usually uses jam, so the cookies may lose shape in the oven. When you take the cookies out of the oven, immediately reshape the cookies using a spoon or your thumb.