Sieve the plain flour, the pinch of salt and the sugar into a bowl, make a well in the centre and drop in the lightly beaten eggs. With a whisk or wooden spoon, starting in the centre, mix the egg and gradually incorporate the flour from the sides. In a separate bowl or jug, mix together the milk and the water. Slowly add the milk and water mixture to the flour and egg mixture and beat it until the batter is covered with bubbles.
Let the batter stand in a cold place for a while - a couple of hours if you have time. Just before you cook the pancakes, stir in the melted butter.
Heat a non-stick pan over a high heat. When it is hot, pour in a small ladleful of batter, or just enough to coat the base of the pan with a thin film. The batter should cook immediately - loosen it around the edges with a rubber fish slice, flip it over and cook the pancake for a few seconds on the other side. Slide the cooked pancake on to a plate, and serve with your chosen filling, either sweet or savoury.