In a large bowl, whisk together the flour, protein powder, sugar, and salt.
Add milk and butter to a microwave-friendly bowl and microwave until the milk heats up, but the butter has not fully melted. Then, using a spoon, stir the milk until the butter fully dissolves. This way, we won’t overheat the milk.
Add the dry yeast to the milk and whisk until it fully dissolves. Then, add in the egg and whisk until smooth.
Now pour the wet ingredients into the dry ones and mix with a rubber spatula until soft dough forms.
Transfer the dough onto a lightly floured surface. Flour your hands and knead the dough for 3-5 minutes. If the dough is too sticky, add more flour. Form a ball of dough and place it in a greased bowl, cover it, and let it sit for about 10 minutes.
In a small bowl, combine brown sugar and cinnamon.
Once 10 minutes pass, roll out the dough into 14x8’’ rectangle.
Spread the butter on top of the dough, and sprinkle all over with the mixture of brown sugar and cinnamon. Now, roll up the dough to make a log and cut it into 10-12 rolls. I did 11.
Lightly grease a 9-inch round cake pan and place the cinnamon rolls, spacing them out evenly.
Cover the cake pan with aluminium foil and a towel, and place it in a warm place so the rolls rise for 60-90 minutes until they double in size.
Preheat the oven to 375°F and bake the cinnamon rolls for 18-22 minutes until they are lightly browned. If the tops are getting too brown too quickly, loosely cover the pan with aluminium foil and continue baking.
While baking, mix together the icing using a mixer.
Once the cinnamon rolls are done, remove from the oven and place them on a rack. Cover with icing and enjoy warm.
Store covered for 1 day at room temperature or for up to 5 days in the fridge.