In a mixing bowl, whisk together 1 cup of all-purpose flour and 1/2 teaspoon of fine sea salt. Create a well in the center, then gradually add 2 large room-temperature eggs and 1 cup of whole milk while whisking until smooth. Incorporate 2 tablespoons of melted unsalted butter and let the batter rest for 30 minutes.

Preheat a nonstick skillet over medium heat and brush it lightly with melted butter. Pour approximately 60 ml of the crêpe batter into the skillet, swirling it to form a thin layer. Cook until the edges begin to lift and turn golden, about 1-2 minutes. Gently flip and cook for an additional 30 seconds.

Take one cooked crêpe and spread a thin layer of Dijon mustard on one side. Layer with 1/4 cup of cooked ham and 1/4 cup of Gruyère cheese. Fold the crêpe into a triangle.

Return the filled crêpes to the skillet over medium heat. Press them down gently to help melt the cheese inside, cooking until the cheese is gooey and the crêpes are crispy, about 1-2 minutes per side.

Plate the crêpes and garnish with freshly chopped parsley and black pepper. Serve with a green salad or crispy roasted potatoes.