Preheat oven to 175°C (350°F) and grease an 8-inch round cake pan.

In a large bowl, whisk together oat flour, chocolate protein powder, cocoa powder, 100g erythritol, baking powder, and 5g instant coffee.

Add Greek yogurt, liquid egg whites, almond milk, and vanilla extract to the dry ingredients.

Mix until a smooth, homogenous batter forms, ensuring no dry pockets remain.

Pour batter into the prepared pan and bake for 22-25 minutes or until a toothpick inserted in the center comes out clean.

Remove from oven and allow the cake to cool completely on a wire rack before frosting.

In a separate narrow bowl, combine 10g instant coffee, hot water, and 25g erythritol.

Using a hand mixer, whip the coffee mixture on high speed for 3 to 5 minutes until stiff, light-colored peaks form.

Gently fold the 15g vanilla protein powder into the whipped coffee foam using a spatula to preserve aeration.

Spread the protein Dalgona frosting over the cooled cake and serve immediately.