In a large bowl, whisk together the eggs, milk, flour and salt into a lumpy batter. Blend using a hand blender, until just smooth. Adjust the batter consistency with a dash of water if needed.
Add the melted butter, and blend until incorporated.
Cover and let the batter rest for 30 minutes.
Heat a knob of butter in a pan over medium heat. Pour in a ladleful of batter, swirling to coat the base. Cook until the surface looks set and no wet patches remain.
Sprinkle the cheese evenly over the crêpe, then place a slice of ham and a pan-fried egg in the center.
Fold in the edges of the crêpe to create a triangle or a square, leaving the yolk visible in the center. Cook for another minute, then serve immediately.