In a mixing bowl, whisk together the flour and fine sea salt. Create a well in the center and add eggs. Gradually pour in the milk while whisking to prevent lumps. Mix in melted butter, and allow to rest for 30 minutes.

Preheat a nonstick skillet over medium heat, brush with melted butter. Pour approximately 60 ml of batter, swirl to form a thin layer. Cook for 1-2 minutes until edges lift, then flip and cook for 30 seconds.

Take a warm crêpe and spread mustard (if using) on one side, layer with ham and cheese. Fold into triangle or half-moon shape.

Return filled crêpe to the skillet, press gently to help cheese melt. Cook for 1-2 minutes on each side until golden brown and cheese is melted.

Remove crêpes and garnish with parsley and black pepper. Serve hot.