In a medium jug whisk together the egg, milk, water and flour until smooth and no lumps remain, about a minute. Heat 2 teaspoons oil in a large frying pan or crepe pan over medium low heat and swirl the oil gently around to cover the base. Pour a quarter of the crepe batter into the middle of the pan and swirl around quickly to cover the base in a thin layer. Return pan to heat and cook for a minute or until the top of the crepe is mostly set. Using a spatula, flip the crepe over and cook for another 30 seconds for the crepe to cook through. Transfer to a large plate and repeat with the remaining batter and crepes.
To make the filling, peel and finely slice onion. Slice mushrooms. Heat butter in a large frying pan and add onion. Cook over medium heat, stirring, for 3 minutes for the onion to become translucent. Add mushrooms, salt and pepper. And cook, stirring for another 3 minutes. Stir in thyme. Add cream and stir though. Turn off the heat.
To serve, top each crepe with the filling mixture and fold over the sides. Grate some Parmesan cheese over the top and sprinkle with nuts.
4 servings