Preheat the oven to 350°F (175°C). Grease the 9x13-inch baking dish.
In a large mixing bowl, combine almond flour, erythritol, cocoa powder, baking powder, and salt. Mix well.
In another bowl, whisk together the eggs, almond milk, melted coconut oil (or butter), and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and mix until well combined.
Spread half of the batter evenly into the prepared baking dish.
In a small bowl, combine the ground cinnamon with a tablespoon of erythritol. Sprinkle this cinnamon mixture evenly over the batter in the baking dish.
Pour the remaining batter over the cinnamon layer and spread gently to cover.
Bake in the preheated oven for about 30 minutes, or until a toothpick inserted into the center comes out clean.
While the cake is baking, prepare the topping by mixing the softened cream cheese, butter, powdered erythritol, and almond milk until smooth and creamy.
Once the cake is done, let it cool for a few minutes before drizzling the topping over the warm cake.