Preheat the oven to 175°C (347°F).
Add dark chocolate and butter to a bowl and melt using a double boiler or a microwave.
In another bowl, mix eggs and erythritol well.
Pour the melted chocolate mixture into the egg mixture and combine.
Add almond flour, cocoa powder, baking powder, and salt. Mix lightly.
Pour half of the batter into the pan.
Layer low-sugar brownie batter and low-sugar cookie batter on top.
Bake in a 180°C (356°F) oven for 20–25 minutes.