Add all ingredients except the egg and the protein powder in to a large bowl and mix vigorously (a hand/stick blender is best but a whisk will do) until fairly smooth (can leave slightly lumpier if preferred).
Add the egg and the protein powder and mix again.
Line a medium sized baking tin or dish with baking parchment and scoop the mixture in. If the mixture doesn't level out by itself, smooth to edges with fork.
Bake in a preheated oven at around 190 °C (170 °C fan assisted) for approximately 20 minutes or until just set.
Note: the mixture will continue to set and dry out as it cools so bear this in mind when checking if cooked.
There are 99 calories in 1 serving of Clean Brownies.