Sift the flour and salt into a large mixing bowl. Make a well in the centre of the flour and break the eggs into it. Whisk the eggs and the flour together and start adding small quantities of milk until the batter is smooth, with the consistency of single cream.
Melt 50g/2oz of butter in a pan. Spoon half of it into the batter and whisk it in, then pour the rest into a bowl and set aside to add to the pan when cooking the pancakes.
Get the pan really hot then turn the heat down to medium. Add about 2 tablespoons of batter to the pan and tip the pan from side to side to get the base evenly coated with batter. The pancake should take 30 seconds to cook. Lift the edge with a palette knife to see if it's golden brown and then flip it over for a few seconds to finish cooking.
Slide out of the pan onto a plate. Sprinkle with gruyere and shredded ham, roll up or fold into quarters and eat straight away.
«You could make this more substantial by placing the filled pancakes in a baking dish, topping with béchamel sauce and grilling until bubbling hot.»