In a mixing bowl, whisk together 1 cup of all-purpose flour and a pinch of salt until well combined. Crack in 2 large eggs, and gradually stir in 1.25 cups of whole milk to achieve a smooth batter. Lastly, mix in 2 tablespoons of melted unsalted butter. Let the batter rest for 30 minutes at room temperature to enhance its texture.

Heat a nonstick skillet over medium heat and brush it lightly with additional melted butter. Pour about 60 ml (or ¼ cup) of the crêpe batter into the skillet, swirling it gently to create a thin layer. Cook the crêpe for 1-2 minutes, or until the edges begin to lift easily, then flip it and cook for another 30 seconds until lightly golden.

Once the crêpes are cooked, spread a thin layer of Dijon mustard (if desired) on one side of each crêpe while they're still warm. Place a generous portion of cooked ham and a sprinkle of Gruyère cheese on top. Fold the crêpe into a triangle or a half-moon shape.

Return the folded crêpe to the skillet and gently press it down with a spatula. Cook for another 1-2 minutes, flipping once, until the crêpe is golden brown and the cheese is melted.

Carefully remove the warm crêpe from the skillet and place it on a serving plate. Garnish with freshly chopped parsley and a crack of black pepper. Serve hot.