Preheat the oven to 350°F (175°C), and line a cake pan with parchment paper.
In a large mixing bowl, combine almond flour, cocoa powder, protein powder, erythritol, baking powder, and salt.
In another bowl, whisk together the eggs, applesauce, and vanilla extract until well combined.
Gradually add the wet ingredients to the dry ingredients, stirring until no dry spots remain.
Pour the batter into the prepared cake pan, smoothing the top with a spatula.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
Once cooled, you can frost or serve as desired, perhaps with a dollop of whipped cream or berries.