In a mixing bowl, whisk together the flour and salt. Make a well, crack in the eggs, and gradually mix in milk and melted butter. Let sit for 30 minutes.

Preheat a nonstick skillet over medium heat and lightly brush with butter. Pour about 60 ml of batter, swirl to form a thin layer, and cook for 1-2 minutes. Flip and cook for 30 seconds.

Spread a thin layer of Dijon mustard on each crêpe. Add ham and Gruyère cheese on one half, then fold to enclose.

Return filled crêpes to the skillet over medium-low heat, press gently and cook for 1-2 minutes per side until golden and cheese is melty.

Serve crêpes arranged on a platter, garnished with chopped parsley and black pepper.