Preheat the oven to 170°C (338°F).
Finely chop the walnuts.
In a bowl, mix almond flour, cacao powder, cinnamon powder, and baking powder.
In another bowl, combine egg, erythritol, and coconut oil.
Mix the dry ingredients with the wet ingredients, then add the chopped walnuts.
Divide the dough into 6 equal pieces, shape them into rounds, and place them on a baking tray.
Bake in the preheated oven for 13–15 minutes.