Combine the granulated sweetener and ground cinnamon in a small bowl for your delicious cinnamon swirl. Set this mixture aside.
Preheat your oven to 325°F (160°C) and lightly grease a 9x9 inch baking pan to prevent sticking.
In a medium mixing bowl, whisk together the almond flour, erythritol sweetener, whey protein powder, baking powder, and salt until well combined.
Next, stir in the eggs, melted butter, and vanilla extract into the dry ingredients.
Pour in the almond milk and continue to mix until your batter is smooth and fully blended.
Spread half of your prepared batter evenly into the bottom of the greased baking pan.
Sprinkle about two-thirds of your cinnamon filling mixture generously over this first layer of batter.
Carefully spread the remaining cake batter over the cinnamon layer, smoothing the top with a knife or an offset spatula.
Bake for 25 to 30 minutes, or until the top turns a lovely golden brown and feels firm when gently touched. Remove from the oven.
While the cake is still warm, brush the top with the extra tablespoon of melted butter and sprinkle the remaining cinnamon filling mixture over it.
Let the cake cool completely in the pan before you even think about frosting it – this step is key for a perfect finish!
In a small bowl, beat the softened cream cheese until it's wonderfully smooth and creamy.
Add the powdered sweetener, heavy whipping cream, and vanilla extract to the cream cheese. Beat again until everything is perfectly combined, smooth, and fluffy.
Once the cake is completely cool, pipe or drizzle this irresistible frosting over the top.
Slice and enjoy your healthy, homemade treat!