Boil the potatoes and then cut them in thin slices.
Cut the onion and Mushrooms in pieces.
In a bowl pour the 2 different flour, add the egg, salt, olive oil and water. Mix well.
Let the batter rest in the fridge for minimum 30 minutes.
Heat up a frying pan and add some butter.
Pour some of the batter in the frying pan and make sure to cover the bottom. Flip the crepe, place cheese, onion and mushroom in the middle of the crepe.
Fold in the edges to the center and serve warm.