How to make
In a bowl, mix the cocoa, flour and salt.
In a separate bowl, beat the eggs, erythritol and vanilla with a mixer. The mixture should be tripled.
In a third bowl, mix the pre-melted butter and chocolate (melt them separately) and then mix them until you have a homogeneous mixture.
In the bowl with the egg mixture, gradually add the dry ingredients, while stirring constantly, until a homogeneous mixture is obtained.
Finally, add the butter and chocolate and mix until you have a homogeneous mixture.
Transfer the mixture into a baking pan covered with baking paper and bake it in a preheated oven at 340°F (170 degrees), with a fan for about 20-25 minutes.