Grate the butter on a coarse grater. Place in a deep bowl.
Separate the whites from the yolks. Place the whites in one bowl and the yolks in another.
Add flour, baking powder, sugar, and salt to the butter. Mix until smooth. Add the yolks and knead the dough.
Cut the bananas into 5 mm thick slices.
Roll out the chilled dough and place it in a baking dish, forming the bottom and sides.
Place bananas on the dough.
Add sour cream on top and bake in the oven for 20 minutes.
Meanwhile, prepare the protein cream. To do this, add powdered sugar to the whites, beat everything together with a mixer until smooth and fluffy.
Remove the pie from the oven, spread the protein cream over the sour cream. Put the pie back in the oven for another 5 minutes, increasing the temperature to 200 ⁰С.
Remove the finished pie from the oven, take it out of the pan and put it in a cool place.
Serve the pie cold, cut into portions.